BITS Faculty Publications

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    Exploiting multiple antenna cognitive radio system for cooperative spectrum sharing
    (IEEE, 2015) Vashistha, Ankush
    This paper proposes a cooperative spectrum sharing scheme in which multiple antennas of a secondary (aka cognitive) system is exploited to nullify the interference from the primary (aka licensed) to secondary system and vice versa. The secondary system also acts as a "decode-and-forward" relay for the primary system thus boosting its performance. The performance of primary and secondary system is analyzed by obtaining the closed form expressions for outage probability. The simulation results are also shown to validate the theoretical expressions obtained in this paper.
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    Outage analysis of a multiple-antenna cognitive radio system with cooperative decode-and-forward relaying
    (IEEE, 2014-12) Vashistha, Ankush
    In this paper, we analyze a two-phase hierarchical spectrum sharing protocol based on cooperative decode and forward relay transmission wherein it is assumed that the cognitive (i.e secondary) system is equipped with multiple antennas. The performance of the licensed (i.e. primary) as well as cognitive system is quantified by deriving the closed form expressions for outage probability. The theoretical and simulation results show that by exploiting multiple antennas at secondary transmitter (ST), we can drastically improve the performance of both primary and secondary systems as compared to conventional spectrum sharing schemes.
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    On the performance of multiple antenna cooperative spectrum sharing protocol under Nakagami-m fading
    (IEEE, 2015-12) Vashistha, Ankush
    In a cooperative spectrum sharing (CSS) protocol, two wireless systems operate over the same frequency band albeit with different priorities. The secondary (or cognitive) system which has a lower priority, helps the higher priority primary system to achieve its target rate by acting as a relay and allocating a fraction of its power to forward the primary signal. The secondary system in return is benefited by transmitting its own data on primary system's spectrum. In this paper, we have analyzed the performance of multiple antenna cooperative spectrum sharing protocol under Nakagami-m Fading. Closed form expressions for outage probability have been obtained by varying the parameters m and Ω of the Nakagami-m fading channels. Apart from above, we have shown the impact of power allocation factor (α) and parameter m on the region of secondary spectrum access, conventionally defined as critical radius for the secondary system. A comparison between theoretical and simulated results is also presented to corroborate the theoretical results obtained in this paper.
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    Bit error rate and outage analysis of an interference cancellation technique for cooperative spectrum sharing cognitive radio systems
    (The Institution of Engineering and Technology, 2016-08) Vashistha, Ankush
    In this study, an overlay spectrum sharing scheme has been proposed for a cognitive radio system. To achieve the desired quality of service for the licenced (i.e. primary) system and spectrum access for unlicenced (i.e. secondary) system, a three-phase cooperative decode and forward relaying is used. Furthermore, space–time block coding is used in order to cancel the interference at primary as well as secondary receiver. It has been shown that the proposed scheme helps in achieving diversity gain of three and two for primary and secondary systems, respectively. The performance of both primary and cognitive (secondary) system is appraised by deriving closed-form expression for bit error rate and outage probability. The theoretical and simulation results validate that the proposed scheme improves the performance of both systems as compared with the earlier proposed schemes.
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    Optimizing Fading-Averaged Bandwidth Efficiency of Underlay Cognitive Radio System by Transmit Power Adaptation
    (IEEE, 2019) Bitragunta, Sainath
    Power 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 efficiency
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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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    Application of Game Theory to Cooperative Underlay Cognitive Radio IoT
    (IEEE, 2019) Bitragunta, Sainath
    Internet of things (IoT) is a new paradigm in wireless communication that offers a host of new opportunities to exploit the finite resources available. Cognitive radio networks (CRNs) employ these spectrum opportunities by using their inherent adaptive nature to automatically detect available channels in the spectrum and change transmission parameters to allow more communications to run concurrently, thus improving overall efficiency. The application of game theoretic principles to solving problems in this domain allows for the creation of fairly realistic models that clearly outline the relationship between the stakeholders involved, under the assumption of rationality. This paper presents a model for an IoT-based CRN in the underlay mode of operation. A triangular lattice with a set of relays is considered to model the secondary user network. The interference and power constraints accounted for in calculating the Nash equilibrium bring the model closer to direct applicability in the real world by including variations depending on channel strength and desirability.
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    A Survey of Energy and Spectrum Harvesting Technologies and Protocols for Next Generation Wireless Networks
    (IEEE, 2021-04) Bitragunta, Sainath; Chamola, Vinay; Joshi, Sandeep
    Energy harvesting (EH) and spectrum harvesting (SH) are two promising and useful green communication and networking mechanisms for the next-generation wireless networks. While the former techniques exploit ambient energy sources to scavenge energy, the latter exploit the unused or moderately used electromagnetic spectrum. With the advent of cyber-physical systems and the Internet-of-Things (IoT), the presence of tens of billions of low power sensor devices would soon be a reality. These small sensing devices would be present in many systems around us, such as home appliances, telecommunication devices, medical electronics, transport systems, etc. These miniaturized, low-power consuming devices may exploit EH and SH techniques for energy storage and communication. These EH-SH-enabled sensors or low-power nodes need to consume very little energy for sensing and communicating opportunistically. However, several theoretical problems and practical challenges exist in EH-SH communications. In this comprehensive survey paper, we first present the historical background of EH, and SH techniques, and their development over several decades. Specifically, we focus on EH-SH communication technologies and protocols for a wide range of systems and networks. We present a detailed survey of the various harvesting techniques and protocols from recent literature. Finally, we describe exciting open, intra-disciplinary, and inter-disciplinary challenges for further research on EH-SH communication technologies.