BITS Faculty Publications
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Item Outage Probability Analysis for UOWC System Over Oceanic Turbulence With Pointing Errors(IEEE, 2023-09) Zafaruddin, S.M.This letter proposes a combined underwater optical wireless communication (UOWC) system consisting of maximum ratio combining (MRC)-based direct link and optical intelligent reflecting surface (OIRS)-assisted indirect link. Oceanic turbulence is modeled by the mixture exponential–generalized gamma (EGG) distribution. We evaluate the system performance using the outage probability. An exact outage probability expression is derived for these links under EGG oceanic turbulence and pointing errors (PEs). Moreover, we derive the asymptotic expression for the outage probability to present an analytical expression of the system’s diversity order. We demonstrate that the Monte Carlo simulation results perfectly match the derived expressions, and closely align with the asymptotic expression at high signal-to-noise ratio (SNR) values. Hence, the proposed system ameliorates the connectivity of the high-speed UOWC under different underwater channel conditions.Item Performance Analysis of Mixed Underwater and Terrestrial OWC Systems Over Foggy Weather(IEEE, 2021) Zafaruddin, S.M.There has been extensive research on the performance of underwater optical wireless communication (UOWC) mixed with terrestrial OWC (TOWC) over atmospheric turbulence with pointing errors considering deterministic path loss under foggy weather conditions. Recent measurement campaigns provide a probabilistic behavior of the signal attenuation over the foggy channel. In this paper, we analyze the performance of a mixed TOWC-UWOC system by considering random foggy channels with pointing errors for the terrestrial link and lognormal distribution for underwater communication. We apply the decode-and-forward (DF) relaying to integrate the two technologies and analyze the performance of the proposed system by deriving analytical expressions of the outage probability, average SNR, and ergodic rate in terms of channel and system parameters. We use measurement data fitted parameters of the random fog and underwater channel to demonstrate the performance of mixed links under various foggy conditions and characteristics of underwater turbulence. We validate our derived mathematical expressions using numerical analysis and Monte Carlo simulations and demonstrate the performance of the relay-assisted mixed link over different foggy conditions and underwater turbulence.Item Simplified Performance Analysis of OWC System Over Atmospheric Turbulence with Pointing Error(IEEE, 2020) Zafaruddin, S.M.Optical wireless communication (OWC) is highly vulnerable to the atmospheric turbulence and pointing error. Performance analysis of the OWC system under the combined channel effects of pointing errors and atmospheric turbulence is desirable for its efficient deployment. The widely used Gamma-Gamma statistical model for atmospheric turbulence, which consists of Bessel function, generally leads to complicated analytical expressions. In this paper, we consider the three-parameter exponentiated Weibull model for the atmospheric turbulence to analyze the ergodic rate and average signal-to-noise ratio (SNR) performance of a single-link OWC system. We derive simplified analytical expressions on the performance under the combined effect of atmospheric turbulence and pointing errors in terms of system parameters. We also derive approximate expressions on the performance under the atmospheric turbulence by considering negligible pointing error. In order to evaluate the performance at high SNR, we also develop asymptotic bounds on the average SNR and ergodic rate for the considered system. We demonstrate the tightness of derived expressions through numerical and simulation analysis along with a comparison to the performance obtained using the Gamma-Gamma model.Item Terahertz Wireless Transmissions with Maximal Ratio Combining over Fluctuating Two-Ray Fading(IEEE, 2022) Zafaruddin, S.M.Mitigating channel fading and transceiver impairments are desirable for high-speed terahertz (THz) wireless links. This paper analyzes the performance of a multi-antenna THz wireless system by considering the combined effect of pointing errors and fluctuating two-ray (FTR) fading model. We provide a statistical characterization of the maximal ratio combining (MRC) receiver over independent and nonidentical (i.ni.d.) channel conditions in terms of multi-variate Fox’s H by deriving density and distribution functions of the signal-tonoise ratio (SNR) of a single-link THz link using incomplete Gamma function. We develop exact analytical expressions of outage probability, average bit-error-rate (BER), and ergodic capacity for both single-antenna and MRC receivers. We also present the diversity order of the system by deriving asymptotic expressions for outage probability and average BER at high SNR to obtain insights into the system performance. We validate our derived analytical expressions with Monte-Carlo simulations and demonstrate the effect of various system and channel parameters on the performance of single and multi-antenna THz wireless communications.Item Fixed-Gain AF Relaying for RF-THz Wireless System Over α-κ-μ Shadowed and α-μ Channels(IEEE, 2022-05) Zafaruddin, S.M.Recent research investigates the decode-and-forward (DF) relaying for mixed radio frequency (RF) and terahertz (THz) wireless links with zero-boresight pointing errors. We analyze the performance of a fixed-gain amplify-and-forward (AF) relaying for the RF-THz link to interface the access network on the RF technology with wireless THz transmissions. We develop probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end SNR for the relay-assisted system in terms of bivariate Fox’s H function considering α - μ fading for the THz system with non-zero boresight pointing errors and α - κ - μ shadowed ( α -KMS) fading model for the RF link. Using the derived PDF and CDF, we present exact analytical expressions of the outage probability, average bit-error-rate (BER), and ergodic capacity of the considered system. We also analyze the outage probability and average BER asymptotically for a better insight into the system behavior at high SNR. We use simulations to compare the performance of the AF relaying having a semi-blind gain factor with the recently proposed DF relaying for THz-RF transmissions.Item Performance of Dual-Hop Relaying for THz-RF Wireless Link(IEEE, 2021-04) Zafaruddin, S.M.The use of Terahertz (THz) frequency bands for data transmissions between the core network and an access point can be promising for next generation wireless systems. In this paper, we analyze the performance of a dual-hop relaying for THz-RF wireless link for backhaul applications. Considering the α−µ fading channel and a statistical model of pointing errors, we derive a novel closed-form expression of the cumulative distribution function (CDF) of the signal-to-noise ratio (SNR) for the THz link, which is also valid for non-integer values of µ. Using the CDF, we derive analytical expressions of the end-to-end SNR and lower bound on ergodic capacity of a decode-and-forward (DF) assisted THz-RF relaying in terms of system parameters. Using analytical results of the direct link and computer simulations, we demonstrate that the THz-RF relaying is a viable technology for wireless backhaul, providing a significant increase of almost 25% in the spectral efficiency, compared to the direct transmissions.Item On the Performance of Multihop THz Wireless System Over Mixed Channel Fading With Shadowing and Antenna Misalignment(IEEE, 2022-11) Zafaruddin, S.M.The existing relay-assisted terahertz (THz) wireless system is limited to dual-hop transmission with pointing errors and short-term fading without considering the shadowing effect. This paper analyzes the performance of a multihop-assisted backhaul communication mixed with an access link under the shadowed fading with antenna misalignment errors. We derive novel probability density and distribution functions of the signal-to-noise ratio (SNR) of the multihop link employing channel-assisted (CA) and fixed-gain (FG) amplify-and-forward (AF) relaying for each hop by considering independent but not identically distributed (i.ni.d) α - μ fading channel with pointing errors. We present analytical expressions for the outage probability and average bit-error-rate (ABER) and develop asymptotic analysis in high SNR regime to derive the diversity order for both CA-multihop and FG-multihop backhaul links. We use the derived results of the multihop systems to analyze the statistical performance of the integrated backhaul-access relaying for both uplink and downlink transmission considering the generalized- K shadowed fading model in the access link. We also present exact and asymptotic expressions of the outage probability for the considered mixed system. We perform computer simulations to provide design and deployment aspects of employing multiple relays to enhance THz wireless transmissions.Item Unified Performance Analysis of Reconfigurable Intelligent Surface Empowered Free-Space Optical Communications(IEEE, 2021-12) Zafaruddin, S.M.Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based technologies such as free-space optical (FSO) communications. In this paper, we analyze the performance of RIS-empowered FSO (RISE-FSO) systems by unifying Fisher-Snedecor ( F ), Gamma-Gamma ( GG ), and Malága ( M ) distributions for atmospheric turbulence with zero-boresight pointing errors over deterministic as well as random path-loss in foggy conditions with heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) methods. By deriving the probability density function (PDF) and cumulative distribution function (CDF) of the direct-link (DL) with the statistical effect of atmospheric turbulence, pointing errors and random fog, we develop exact expressions of PDF and CDF of the resultant channel for the RISE-FSO system. Using the derived statistical results, we present exact expressions of outage probability, average bit-error-rate (BER), ergodic capacity, and moments of signal-to-noise ratio (SNR) for both DL-FSO and RISE-FSO systems. We also develop an asymptotic analysis of the outage probability and average BER and derive the diversity order of the considered systems. We validate the analytical expressions using Monte-Carlo simulations and demonstrate the performance scaling of the FSO system with the number of RIS elements for various turbulence channels, detection techniques, and weather conditions.Item Performance of Dual-Hop Relaying for THz-RF Wireless Link Over Asymmetrical α-μ Fading(IEEE, 2021-10) Zafaruddin, S.M.Terahertz (THz) frequency bands can be promising for data transmissions between the core network and access points (AP) for next-generation wireless systems. In this paper, we analyze the performance of a dual-hop THz-RF wireless system where an AP facilitates data transmission between a core network and user equipment (UE). We consider a generalized model for the end-to-end channel with independent and not identically distributed (i.ni.d.) fading model for THz and RF links using the α - μ distribution, the THz link with pointing errors, and asymmetrical relay position. We derive a closed-form expression of the cumulative distribution function (CDF) of the end-to-end signal to noise ratio (SNR) for the THz-RF link, which is valid for real-valued μ for a generalized performance analysis over THz fading channels. Using the derived CDF, we analyze the performance of the THz-RF relayed system using decode-and-forward (DF) protocol by deriving closed-form expressions of outage probability, moments of SNR, average BER, and a tight approximation of ergodic capacity in terms of system parameters. We develop asymptotic analysis on the ergodic capacity, outage probability, and average BER in the high SNR region and derive the diversity order of the system. We also analyze the considered system with an i.i.d. model and develop simplified performance to provide insight on the system behavior analytically under various practically relevant scenarios. Simulation and numerical analysis show a significant effect of fading parameters of the THz link and a nominal effect of normalized beam-width on the performance of the relay-assisted THz-RF system.Item Performance analysis of optical wireless communications with aperture averaging over exponentiated Weibull turbulence with pointing errors(Elsevier, 2021-12) Chaubey, V.K.; Zafaruddin, S.M.Aperture averaging (AA) is a potential technique to reduce the effect of atmospheric turbulence in optical wireless communications (OWC). Although there is significant research on point-like detectors, there is a gap in the study on the analytical performance evaluation of OWC systems with AA over atmospheric turbulence and pointing errors. In this paper, we analyze the performance of a single-link OWC system by considering the three-parameter exponentiated Weibull (EW) model for the atmospheric turbulence and the zero boresight fading model for pointing errors. We derive analytical expressions for moments of signal-to-noise ratio (SNR), ergodic capacity, outage probability, average bit-error-rate (BER), and average energy consumption under the combined effect of atmospheric turbulence and pointing errors in terms of system parameters. To provide insights on the system behavior, we develop asymptotic bounds at high SNR on the performance of the considered system. We also derive analytical expressions for the performance of OWC system under the atmospheric turbulence with negligible pointing errors. We demonstrate the performance of OWC system over EW turbulence with a comparison to the performance obtained using the Gamma–Gamma (GG) model and demonstrate the tightness of the derived performance bounds through numerical and simulation analysis.