sarbani ghose | Indian Institute of Technology Delhi (original) (raw)

Papers by sarbani ghose

ICASSP 2023 - 2023 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

In this paper, we have considered a dual-hop wireless network consisting of a decode-and-forward ... more In this paper, we have considered a dual-hop wireless network consisting of a decode-and-forward (DF) relay in presence of an eavesdropper. Relay can correctly decode and retransmits only if the received signal-to-noise ratio (SNR) meets a particular threshold. The eavesdropper has the ability to tap signals from the relay as well as from the source. The performance of the maximal ratio combining (MRC) and selection combining (SC) diversity at the eavesdropper is investigated. Whether knowledge of channel state information (CSI) at the transmitter is known or not is considered for the performance evaluation in secrecy outage probability and ergodic secrecy rate. Asymptotic analyses for the performances are provided. It is shown that direct link has a significant impact on system secrecy. It is found that secrecy performances are the best if the relay is always able to decode correctly. It is also found that knowledge of CSI can help to achieve better secrecy at lower rate. It is observed that unbalance created due to constraint on either of the source-relay link average SNR or relay-destination link average SNR does not yield similar secrecy outage performance but both can limit the secrecy outage performance. On the contrary it is found that only source-relay link quality can limit the ergodic secrecy rate performance.

2013 National Conference on Communications (NCC), 2013

ABSTRACT Achieving security at the physical layer in the presence of eavesdropper has always rema... more ABSTRACT Achieving security at the physical layer in the presence of eavesdropper has always remained a critical issue under adverse channel conditions. The present scenario has relay with multiple antenna to combat channel effects. We have designed system model so that the nodes cooperate among themselves for the available power, with the aim to minimize the total transmit power, under a secrecy rate constraint. Here the relay sends out a jamming signal in order to confuse the eavesdropper. We assume correlated fading in the relay channels. The channel is modeled taking into account the large scale fading and small scale fading as well, through inclusion of path loss exponent and Rayleigh fading effects. The optimal power requirements for the source and the jammers are determined subject to the constraint of secrecy rate. The power allocation also depends upon path loss exponent, distance and fading parameters. The corresponding relaying regions have been plotted for real, equal and real, unequal roots of source power. Real, equal roots of source power are independent of position of relay. From the simulations we observe that the region expands when relays are away from the source.

2014 IEEE Workshop on Statistical Signal Processing (SSP), 2014

ABSTRACT In this paper, we consider a two-hop wireless system consisting of one source, one desti... more ABSTRACT In this paper, we consider a two-hop wireless system consisting of one source, one destination, one eavesdropper and multiple amplify-and-forward relays. A time-division duplex scheme is proposed that aims at minimizing the secrecy rate outage by selecting an optimal relay from the set of candidate relays. In the first time slot, the source transmits the information bearing signal, meanwhile the destination jams the eavesdropper. In the second slot, the selected relay forwards the received signals in amplify-and-forward fashion. Out of two hops, the eavesdropper can tap only the signal transmitted by the relay in the second hop. We obtain a closed-form expression of the end-to-end secrecy outage for instantaneous and statistical channel-state information of the eavesdropper. The analytical results suggest that the proposed destination-based jamming outperforms the conventional relay selection scheme without jamming. Monte Carlo simulations are performed to verify the analytical results.

IEEE Access, 2019

This paper investigates the security performance of two relay selection schemes for cooperative n... more This paper investigates the security performance of two relay selection schemes for cooperative non-orthogonal multiple access (NOMA) systems, where K randomly distributed relays are employed with either decode-and-forward (DF) or amplify-and-forward (AF) protocols. More particularly, twostage relay selection (TRS) and optimal relay selection (ORS) schemes are taken into considered. To characterize the secrecy behaviors of these RS schemes, new closed-form expressions of both exact and asymptotic secrecy outage probability (SOP) are derived. We confirm that the SOP of TRS scheme is equal to that of ORS scheme for DF/AF-based NOMA systems. Based on analytical results, the secrecy diversity orders achieved by the pair of RS schemes for DF/AF-based NOMA systems are K, which are equal to the number of relays. It is shown that the secrecy diversity orders for the cooperative NOMA systems are determined by the number of the relays. Numerical results are presented to demonstrate that: 1) The secrecy performance of AF-based NOMA system outperforms that of DF-based NOMA system, when not all DF relays successfully decode the received information; 2) With the number of relays increasing, the SOP of these RS schemes for DF/AF-based NOMA systems becomes lower; and 3) The TRS/ORS schemes are capable of achieving better secrecy outage behaviors compared to random RS and orthogonal multiple access based RS schemes.

We analyze secrecy of a dual-hop cooperative system consisting of multiple decode-and-forward rel... more We analyze secrecy of a dual-hop cooperative system consisting of multiple decode-and-forward relays in delay-constrained environment using rateless code, where there exists a separate time limit for both the hops. During the first hop, source carries out rateless coded transmission in the allotted time. Relay nodes which have successfully acquired target entropy forwards the information to the destination in the given time limit, using same rateless code at each node. Simultaneous transmissions by these relay nodes leads to faster accumulation of energy at the destination thereby reducing the decoding time. We have derived a closed-form expression of the average time for the first phase which allows fixed number of relays to decode the information. Analysis for achieving the time limit by these relays in the second phase has also been evaluated. Simulation results show that there exist an optimal number of decoding relays that leads to the lowest expenditure of the total time. Furt...

GLOBECOM 2017 - 2017 IEEE Global Communications Conference, Dec 1, 2017

In this paper, we consider an active eavesdropping scenario in a cooperative system consisting of... more In this paper, we consider an active eavesdropping scenario in a cooperative system consisting of a source, a destination, and an active eavesdropper with multiple decode-andforward relays. Considering an existing assumption in which an eavesdropper is also a part of network, a proactive relay selection by the eavesdropper is proposed. The best relay which maximizes the eavesdropping rate is selected by the eavesdropper. A relay selection scheme is also proposed to improve the secrecy of the system by minimizing the eavesdropping rate. Performances of these schemes are compared with two passive eavesdropping scenarios in which the eavesdropper performs selection and maximal ratio combining on the relayed links. A realistic channel model with independent non-identical links between nodes and direct links from the source to both the destination and eavesdropper are assumed. Closed-form expressions for the secrecy outage probability (SOP) of these schemes in Rayleigh fading channel are obtained. It is shown that the relay selection by the proactive eavesdropper is most detrimental to the system as not only the SOP increases with the increase in the number of relays, but its diversity also remains unchanged.

Internet Technology Letters

IEEE Access

This paper considers secrecy of a three node cooperative wireless system in the presence of a pas... more This paper considers secrecy of a three node cooperative wireless system in the presence of a passive eavesdropper. The threshold-selection decode-and-forward (DF) relay is considered, which can decode the source message correctly only if a predefined signal-to-noise ratio (SNR) is achieved. The effects of channel state information (CSI) availability on secrecy outage probability (SOP) and ergodic secrecy rate (ESR) are investigated, and closed-form expressions are derived. Diversity is achieved from the direct and relaying paths both at the destination and at the eavesdropper by combinations of maximalratio combining (MRC) and selection combining (SC) schemes. An asymptotic analysis is provided when each hop SNR is the same in the balanced case and when it is different in the unbalanced case. The analysis shows that both hops can be a bottleneck for secure communication; however, they do not affect the secrecy identically. While it is observed that CSI knowledge can improve secrecy, the amount of improvement for SOP is more when the required rate is low and for ESR when the operating SNR is also low. It is also shown that the source to eavesdropper link SNR is more crucial for secure communication.

IEEE Transactions on Wireless Communications, 2015

In this paper, we consider a two-hop wireless system consisting of one source, one destination, o... more In this paper, we consider a two-hop wireless system consisting of one source, one destination, one eavesdropper and multiple amplify-and-forward relays. A time-division duplex scheme is proposed that aims at minimizing the secrecy rate outage by selecting an optimal relay from the set of candidate relays. In the first time slot, the source transmits the information bearing signal, meanwhile the destination jams the eavesdropper. In the second slot, the selected relay forwards the received signals in amplify-and-forward fashion. Out of two hops, the eavesdropper can tap only the signal transmitted by the relay in the second hop. We obtain a closed-form expression of the end-to-end secrecy outage for instantaneous and statistical channel-state information of the eavesdropper. The analytical results suggest that the proposed destination-based jamming outperforms the conventional relay selection scheme without jamming. Monte Carlo simulations are performed to verify the analytical results.

Achieving security at the physical layer in the presence of eavesdropper has always remained a cr... more Achieving security at the physical layer in the presence of eavesdropper has always remained a critical issue under adverse channel conditions. The present scenario has relay with multiple antenna to combat channel effects. We have designed system model so that the nodes cooperate among themselves for the available power, with the aim to minimize the total transmit power, under a secrecy rate constraint. Here the relay sends out a jamming signal in order to confuse the eavesdropper. We assume correlated fading in the relay channels. The channel is modeled taking into account the large scale fading and small scale fading as well, through inclusion of path loss exponent and Rayleigh fading effects. The optimal power requirements for the source and the jammers are determined subject to the constraint of secrecy rate. The power allocation also depends upon path loss exponent, distance and fading parameters. The corresponding relaying regions have been plotted for real, equal and real, unequal roots of source power. Real, equal roots of source power are independent of position of relay. From the simulations we observe that the region expands when relays are away from the source.

Microwaves, Communications, Antennas …, Nov 7, 2011

__ The omnipresent wireless medium provides high mobility, yet the very nature of open medium int... more __ The omnipresent wireless medium provides high mobility, yet the very nature of open medium introduces vulnerability. Earlier designs of security mechanisms concentrated more on the upper layers, but physical layer techniques have recently gained popularity. Security is taken care of by maximizing the information rate of the signal sent from the source to the receiver, with an assumption that the eavesdropper's channel is worse than the main channel. User cooperation scheme is utilized to jam the eavesdropper's signal. We have considered a channel model including the path loss exponent and Rayleigh fading, with an aim to maximize secrecy rate under transmit power constraint. Simulations have been done for the secrecy rate in different environments and also how it varies with the position of the receiver and eavesdropper. Index Terms __ physical layer, path loss exponent, Rayleigh fading, secrecy rate, user cooperation.