This paper investigates a multiple-input multiple-output dual-hop underwater visible light communication (UWVLC) system with decode and forward (DF) relay, considering turbulence-induced fading and path loss. Our research aims to analyze the performance of this system under weak oceanic turbulence, featuring M laser sources at the transmitter and N detectors at the destination. We model the UWVLC channel using a log-normal distribution and employ one laser diode and one photodetector at the relay. By selecting the optimal laser source and photodetector based on maximum instantaneous signal-to-noise ratio (SNR), we derive the cumulative distribution function (CDF) of the end-to-end SNR. Utilizing this CDF expression, we provide closed-form expressions for outage probability and average symbol error probability (ASEP) using Gauss–Hermite quadrature techniques for the rectangular quadrature amplitude modulation scheme. We analyze ASEP for different constellation points with M sources and N photodetectors and present simulation results demonstrating ASEP versus average SNR, as well as outage probability versus average SNR, showcasing close agreement with analytical predictions. Moreover, we offer insights for system designers by presenting a trade-off between constellation points and the number of lasers, along with the number of photodetectors, to optimize system performance.
Visible light communication (VLC) has gained attention due to its ability to provide a high data rate in underwater communication. We consider an underwater VLC (UWVLC) system and vertical propagation through the column of water with L layers (channels) and M relays between the transmitter and the receiver. We consider the real-time adverse effects of depth-dependent weak turbulence and path loss. We model each of the L channels with a log-normal distribution, where its statistical parameters mean and variance are functions of the parameters representing the adverse effects of the turbulence. For this concatenated L layered UWVLC, using Gauss–Hermite integral technique, we derive closed-form expressions of outage probability and average symbol error probability taking square quadrature amplitude modulation and rectangular quadrature amplitude modulation modulations with different configurations and assuming imperfect channel state information available at the receiver for detection. We have observed that there is a drastic degradation in the performance as the depth (distance between the transmitter and the receiver) is increased. However, the severity can be alleviated by installing multiple relays between the transmitter and the receiver.
Visible light communication (VLC) has the ability to provide a high data rate up to Mbps in underwater environments for real-time communication systems. In underwater VLC (UWVLC), two major impairments are the turbulence-induced fading due to variation of salt and temperature of seawater and incremental path loss with distance due to absorption and scattering. We consider these two impairments and derive the closed form expressions for average symbol error probability (ASEP), asymptotic relative diversity order, and ergodic capacity for UWVLC dual-hop cooperative communication system. We consider multiple receiver branches with selection combining to combat the effect of fading. The impact of temperature on the fading parameters and system performance is highlighted. We conduct a comparative analysis of ASEP for four-pulse amplitude modulation and four-square quadrature amplitude modulation schemes and draw useful insights. We prove the accuracy of the derived analytical expression using Monte Carlo simulations.
The landforms always withhold the imprints of characteristic geomorphic processes within it. In the upper reaches of Baspa valley, geomorphic records of glacial origin have been investigated for three glaciers viz., Shaune Garang glacier (North facing), Jorya Garang glacier (North facing) and Saro glacier (South facing). The field investigation was carried out for Shaune Garang glacier and extrapolated for Gor Garang and Saro glacier. This terrain is inaccessible and characterized by highly rugged and adverse climatic conditions. Visual interpretation technique of remote sensing is found to be accurate, economical and time saving, hence, the glacial landforms were mapped from Liss III + Pan merged data of IRS 1D, October 2001. The hanging valleys, terminal moraines and lateral moraines are found to be one of the important geomorphic indicators for reconstruction of paleo-glacial history of Baspa valley. The results show that maximum of three sets of lateral and terminal moraines have been identified in Shaune Garang glacier, Jorya garang shows three sets of terminal and two set of lateral moraine and Saro glacier shows one terminal moraine and two sets of lateral moraine indicating respective stages of deglaciation. The length of surface accumulation observed in above data of Oct, 2001 for Shaune Garang, Jorya Garang and Saro glacier is 3.75km, 11.6km and 1.17km respectively. Thus, it shows that south facing glaciers show minimum surface accumulation as compared to the north facing glacier and maximum three stages of deglaciation have been recorded in present study.
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