BITS Faculty Publications

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Subject: search.filters.subject.Fading channels

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    IRS-assisted access link-based multihop THz communication
    (IEEE, 2024) Vashistha, Ankush
    This paper proposes an amplify-and-forward (AF)-based multihop THz backhaul communication integrated with an access THz link. The access link is assisted with an intel-ligent reflecting surfaces (IRS) with an aim to deal with the impediments in THz communication environment. The statistical analysis is presented by deriving the probability density function (PDF) and cumulative distribution function (CDF) of the in-stantaneous signal-to-noise ratio (SNR) for the proposed system. The combined effect of path loss, atmospheric attenuation, and generalized fading is considered for modelling the THz channel. Furthermore, with the aid of PDF and CDF statistics, we propose the exact expressions for outage probability and develop asymptotic analysis in high SNR regime. The simulations are presented to validate the exact analysis and to study various design aspects for the proposed system.
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    Multiple antenna-based THz communication system with channel correlation
    (IEEE, 2024) Vashistha, Ankush
    To minimize environmental impairments and channel fading in the THz band, this paper examines a multiple antenna-based THz communication system. The combined effects of path loss, molecular absorption, and statistical fading are considered for the THz system. A comprehensive correlation structure is utilized that uniquely determines the joint probability density function of the THz channel model. The considered correlation structure is a generalization of the correlation models based on hyper-power or power-correlation. The statistical characterizations of channel correlation for the combining schemes such as maximal ratio combining (MRC), selection combining (SC), and equal gain combining (EGC) are presented at the THz receiver. The asymptotic expressions are proposed for the outage probability for the mentioned diversity schemes. The obtained expressions are expressed in closed-form and are highly accurate in the high signal-to-noise ratio (SNR) region. From the analysis, diversity order and degradation due to correlation are determined. The obtained asymptotic expressions enable the easy estimation of the performance especially for more number of antennas, where Monte Carlo simulation takes a long time to execute. Additionally, presented results reveal the factors that can be utilized to optimize the system performance.
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    An Exact Statistical Representation of α−η−κ−μ Fading Model for THz Wireless Communication
    (IEEE, 2023-12) Zafaruddin, S.M.
    The α−η−κ−μ is one of the most generalized and flexible channel models having an excellent fit to experimental data from diverse propagation environments. The existing statistical results on the envelope of α−η−κ−μ model contain an infinite series, prohibiting its widespread application in the performance analysis of wireless systems. This paper employs a novel approach to derive density and distribution functions of the envelope of the α−η−κ−μ fading channel without an infinite series approximation. The derived statistical results are presented using a single Fox's H-function for tractable performance analysis, especially for high-frequency mmWave and terahertz wireless transmissions. We also develop an asymptotic analysis using the Gamma function, which converges to the exact values within a reasonable range of channel parameters. To further substantiate the proposed analysis, we present the exact outage probability and average bit-error-rate (BER) performance of a wireless link subjected to the α−η−κ−μ fading model using a single trivariate Fox's H-function. We obtain the diversity order of the system by analyzing the outage probability at a high signal-to-noise (SNR) ratio. We use simulations to demonstrate the significance of the developed statistical results compared with the existing infinite series representation of the α−η−κ−μ model.
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    Relay Selection, Eavesdropper-Aware Relaying, PHY-Secrecy Capacity Analysis of Cooperative Wireless System over Hybrid Fading Channels
    (IEEE, 2023) Bhatia, Ashutosh; Bitragunta, Sainath
    Physical layer (PHY) security (PLS) exploits the randomness of wireless fading channels and offers better secrecy capacity. Cooperative and eavesdropper-aware relays are useful in establishing reliable and energy-efficient communication links between the source transmitter and destination receiver and enhancing PHY secrecy. We consider a four-node, two-hop cooperative PHY-security model with one eavesdropper node. For it, we propose relay selection probabilistically and relaying in the presence of hybrid fading channels. We derive closed-form expressions for probabilities with which the regenerative relay is selected. Further, we develop an analysis of PHY-secrecy capacity and gain useful insights. We evaluate and validate the performance of the proposed strategy and present different numerical results. The proposed model with the relay selection and energy-efficient relaying strategy is a useful potential benchmark for more complex power-adaptive cooperative PHY-secure systems and networks.
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    Opportunistic interference alignment in multi-user MIMO Cognitive Radio Networks for different fading channels
    (IEEE, 2016-03) Garg, Sukriti
    Opportunistic interference alignment (OIA) is a well known precoding technique that uses interference alignment to improve the rate of secondary user (SU) simultaneously nullifying the interference that SU causes to a primary user (PU). In this paper, we analyse the efficacy of OIA technique in multi-user multiple input multiple output (MU-MIMO) underlay cognitive radio network (CRN) for generalized κ - μ fading channel and Rayleigh fading with lognormal shadowing (K fading) channel models. Numerical results are presented for the achievable data rates of both PU and SU links in two fading environments.
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    Fading Averaged-Spectral Efficiency Analysis of Average Interference-Constrained, Cooperative Device-to-Device Communication System
    (IEEE, 2017) Bitragunta, Sainath
    We consider a two hop cooperative device-to-device (D2D) communication system. In it, a non-regenerative relay is subject to a tight constraint on the average interference it to the base station (BS). We derive interference-aware, spectral efficiency optimal relay amplification policy as a function of its local fading gains. We then derive expressions for fading-averaged spectral efficiency and its upper bound, and, present numerical results wherein we compare optimum amplification policy with fixed-amplification policy, and, also with a non-cooperative link. In all performance plots, we show that the optimal policy delivers superior performance when compared to fixed-amplification policy, and, non-cooperative link.
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    Fading-Averaged Symbol Error Probability Analysis of Full Duplex Amplify-and-Forward Relaying over Rayleigh Fading Channels
    (IEEE, 2018) Bitragunta, Sainath
    Half-duplex amplify-and-forward (AF) relay based cooperation has been studied in the literature given its simplicity and practicality. In this paper, we consider a full-duplex relay-assisted AF cooperation model. For it, we analyze the fading-averaged symbol error probability (FA-SEP). Specifically, we derive an expression for exact FA-SEP. To get more insights, we derive tractable upper bound for the exact FA-SEP. Furthermore, we extend our analysis and derive asymptotic FA-SEP in a scaling regime. Finally, we present numerical results to validate our analysis. Our analysis of FA-SEP provides a theoretical benchmark and is useful for analyzing more complex cooperative systems employing multiple full-duplex AF relays.
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    Energy Harvesting Cooperative Wireless Systems: Probabilistic Modeling and Statistical Analysis
    (IEEE, 2019) Bitragunta, Sainath
    In this work, we consider a two-hop cooperative wireless system that consists of multiple energy harvesting (EH) relays. The system uses a time-switching based relaying protocol for EH and information processing at the amplify-and-forward (AF) relay nodes. For it, we formulate an order statistics problem of finding the distribution of maximum energy harvested among several EH relay nodes by considering two different fading models, namely, path loss and Rayleigh fading model, path loss and shadow fading model. For these models, we derive analytical expressions for the mean value of maximum harvested energy distribution. Furthermore, we also present an insightful outage analysis and numerical results to validate the analytical expressions. The analysis that we present lead to an essential application of the best EH relay selection in EH cooperative wireless systems and networks.
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    Doubly Constrained Underlay Cognitive Radio System: Optimization and Analysis
    (IEEE, 2019) Bitragunta, Sainath
    In this paper, we consider a doubly constrained underlay cognitive radio (CR) system. In it, a secondary user (SU) transmitter (Tx) is subject to average interference constraint, and spectral efficiency constraint. For the underlay system, we investigate both average energy efficiency and average spectral efficiency. Specifically, we develop an algorithm that determines the suboptimal operating point of transmit power with which the SU-Tx must operate for maximum energy efficiency. We derive an analytical expression for the fading-averaged spectral efficiency assuming Rayleigh fading with path loss and shadowing. To validate the analytical results, we simulate the model in MATLAB using Monte-Carlo simulations and investigate the system performance. The analysis that we present is useful for constrained cognitive radio systems and networks.
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    Comparative Performance Investigation of MIMO-OTFS and MIMO-OFDM using Deep Neural Network Modeling
    (IEEE, 2021) Bitragunta, Sainath
    We consider two popular wireless physical layers (PHYs), namely, multi-input multi-output (MIMO)-orthogonal frequency division multiplexing (OFDM) and MIMO-orthogonal time frequency and space (OTFS) modulation. For them, we develop and implement a deep neural network (DNN) model for fading channel estimation and investigate the mean square error (MSE) performance. While MIMO offers spatial multiplexing to enhance data rates, OFDM provides diversity to combat intersymbol interference. However, OFDM has limitations in high Doppler environments. The OTFS modulation, a newly developed two-dimensional modulation scheme, overcomes OFDM’s limitations. The OTFS modulation technique is helpful in high Doppler fading channels and offers several advantages. In the high Doppler scenario, we find that the OTFS outperforms the OFDM modulation scheme. The added benefit of OTFS over OFDM lies in exploiting channel diversity better in both the time domain and frequency domain when we employ the technique with appropriate equalizers. We show via simulations that DL-enabled MIMO-OTFS DNN exhibits a minimum MSE of value 0.4246, which is less than that of MIMO-OFDM DNN, which is 0.5355 for fading scenarios with high Doppler. Furthermore, we compare our DNN model with the existing linear interpolation technique for channel estimation in MIMO-OTFS at high Doppler.