BITS Faculty Publications
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Item Environment-Aware Green UAV-Assisted, CubeSat Communication Network Energy Efficiency and Outage Probability Analysis(IEEE, 2024-08) Bitragunta, SainathRapid advancements in internet-of-things (IoT), unmanned aerial vehicles (UAVs), and energy harvesting (EH) technologies can be leveraged to design and develop green and reliable cooperative Cube satellite communication (CSC) systems and networks. In this work, we propose a novel cooperative CSC system model comprising green UAVs as intelligent relays equipped with IoT sensors, intelligent processing and EH modules, and transceivers. Using a novel and intelligent probabilistic transmission policy (PTP) that we propose, CubeSats can conserve energy by deactivating transmissions in unfavorable weather conditions based on control signals from the smart UAV via a telemetry link. We extend this model to include multiple CubeSats and analyze it by deriving and evaluating network energy efficiency and its lower bound. Our numerical plots show that the proposed PTP significantly outperforms the continuous transmission policy (CTP). At a specific transmission probability of 0.125, PTP is 40 times more energy efficient than CTP. We extend the work and develop a novel and insightful performance analysis for energy efficiency outage (EEO) probability. Specifically, we derive closed-form approximate expressions for EEO probability and present numerical results. Furthermore, we analyze the performance of clustered CSC networks and present numerical results to assess EEO probability, providing valuable insights for future large-scale green CSC network design and deployment.Item Optimizing Fading-Averaged Bandwidth Efficiency of Underlay Cognitive Radio System by Transmit Power Adaptation(IEEE, 2019) Bitragunta, SainathPower adaptation has been widely studied in the literature, given its significance in designing power efficient adaptive wireless systems. Specifically, transmit power adaptation is an important technique that is naturally appealing for underlay cognitive radio systems, which are intelligent and reconfigurable. In this paper, we consider a secondary underlay transmitter whose transmissions are constrained by an average interference threshold, also it adapts its transmit power as a function of its local channel state information (CSI). In this paper, we derive the optimal power adaptation factor (PAF) that maximizes the fading-averaged bandwidth efficiency (FABE) and also calculate the corresponding energy efficiency. We develop insightful analysis for average spectral efficiency, that is, FABE and energy efficiency for two scenarios: i). CSI-independent PAF and ii). CSI-dependent PAF. Our numerical results reveal that FABE for transmit power adaptation with CSI-dependent PAF delivers superior performance than the PAF that does not depend on instantaneous CSI at the expense of slight decrease in energy efficiencyItem Doubly Constrained Underlay Cognitive Radio System: Optimization and Analysis(IEEE, 2019) Bitragunta, SainathIn 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.Item STPAP: Source Transmit Power Adaptation Policy for Collaborative Wireless Systems(IEEE, 2020) Bitragunta, SainathFor the design of energy-efficient or green communication systems and networks, power adaptation has been studied extensively in the literature. A vital aspect of the same is to minimize the usage of resources wherever possible. This research implements a Source Transmit Power Adaptation Policy (STPAP) for a two hop collaborative wireless communication system. Our objective is to optimize end-to-end fading averaged-energy efficiency (FA-EE) when the source is subject to an average source power constraint. Specifically, we derive an analytical expression for FA-EE in terms of source power, which is adapted as a function of fading channels' state information (CSI). We compare optimal FA-EE results with CSI-independent, fixed source power FA-EE and verify through Monte-Carlo (MC) simulations and analytical results. We find that the proposed STPAP delivers superior performance in terms of FA-EE. We further extend our benchmarking to a scenario where a direct link between source and destination is absent. We also compare optimal FA-EE with fixed power FA-EE and quantify the proposed policy's performance gains.Item Green Satellite Communication Link Design, Optimization, and Performance Analysis(IEEE, 2020) Bitragunta, SainathThe explosive growth in high data rate applications has led to increased satellite communication systems and network energy requirements. Therefore, it is essential to design green or energy-efficient satellite communication links to utilize limited energy sources. In this paper, we consider the low earth orbit (LEO) satellite links and investigate energy efficiency optimization and energy efficiency-outage probability. Specifically, we obtain insightful inequalities for the end-to-end energy efficiency of satellite links. We then investigate the energy efficiency (EE) and outage probability based on EE. Considering typical LEO satellite link parameters, we numerically investigate its performance and determine optimal transmit power to achieve maximum energy efficiency. We believe that this study is useful for designing optimal green satellite communication links in low earth orbits.Item Energy Efficiency Performance Analysis of Single and Multi-Receive Antenna Backscatter Communication System(IEEE, 2022) Bitragunta, SainathAmbient backscatter communication (AmBSC) via ambient energy harvesting passive tags is helpful in the passive internet of things (IoT). Since energy is a limited resource, energy-efficient BSC is essential in passive IoT and could provide long-term profitability. We first consider a simple three-node BSC system set up with a single tag node. In it, all nodes have a single transceiving antenna. We analyze the BSC link's energy efficiency performance over the frequency-flat Rayleigh fading channels for this model. Specifically, we derive analytical expressions for average energy efficiency for the ambient BSC. We then consider an ambient BSC system having a receiver with multiple antennas with antenna selection. For this complex BSC system model, we analyze and evaluate average energy efficiency. We validate derived analytical results using Monte-Carlo simulations. In addition to exact energy efficiency, we also derive its upper bound. The detailed analysis and new insightful results that we present are helpful to design and optimize ambient BSC systems in terms of energy efficiency.Item Hybrid RIS-assisted Cooperative Communication Model Design and Performance Analysis(IEEE, 2022) Bitragunta, SainathThe spectral efficiency and energy efficiency are well-studied performance measures of the next-generation wireless systems and networks. Recently, researchers found dynamically controlled electronic meta-surfaces or reconfigurable intelligent surfaces (RIS) as useful means to enhance these performance measures, specifically, energy efficiency, in the absence of a direct transmission path. Passive meta-surfaces can only reflect their received signals without amplifying, whereas active meta-surfaces can amplify and reflect. This paper proposes a hybrid, dual RIS-assisted cooperative wireless system (CORISS) with two non-Line of sight paths, one via active RIS and the other via passive RIS. We also propose a novel performance objective function (POF) that depends on each path’s spectral efficiency and energy efficiency with an average power constraint. We investigate the proposed hybrid CORISS system via numerical simulations. Our simulations show that the energy efficiency of the active RIS path is inferior to the passive RIS path in high SNR scenarios.Item Energy efficient and delay-constrained sleep period optimization for green radio communication(Elsevier, 2018-10) Bitragunta, SainathGreen communication technology research deals with the methods to achieve efficient energy utilization by radio communication devices. Recent advances in this area include radio resource optimization, radio resource management, and optimal sleep control. In this paper, we focus on the problem of optimizing mean cost subject to a constraint on sleep period. We solve this problem and find the optimal solution to the sleep period and investigate the behavior of the optimum sleep period and the standard deviation of the cost function. We then present numerical results for optimum sleep period, and statistical parameters, namely, standard deviation, and deviation figure. This work not only models mean cost optimally but also compares with ad hoc average costs, which do not account both energy consumption and delay.