Papers by Sanket Kalamkar
We focus on a scenario where two wireless source nodes wish to exchange confidential information ... more We focus on a scenario where two wireless source nodes wish to exchange confidential information via an RF energy harvesting untrusted two-way relay. Despite its cooperation in forwarding the information, the relay is considered untrusted out of the concern that it might attempt to decode the confidential information that is being relayed. To discourage the eavesdropping intention of the relay, we use a friendly jammer. Under the total power constraint, to maximize the sum-secrecy rate, we allocate the power among the sources and the jammer optimally and calculate the optimal power splitting ratio to balance between the energy harvesting and the information processing at the relay. We further examine the effect of imperfect channel state information at both sources on the sum-secrecy rate. Numerical results highlight the role of the jammer in achieving the secure communication under channel estimation errors. We have shown that, as the channel estimation error on any of the channels increases, the power allocated to the jammer decreases to abate the interference caused to the confidential information reception due to the imperfect cancellation of jammer's signal.
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We consider a spectrum sharing scenario where a secondary transmitter (ST) communicates with its ... more We consider a spectrum sharing scenario where a secondary transmitter (ST) communicates with its destination via a decode-and-forward secondary relay (SR) in the presence of interference from multiple primary transmitters. The SR harvests energy from received radio-frequency signals that include primary interference and uses it to forward the information to the secondary destination. The relay adopts a time switching policy that switches between energy harvesting and information decoding over the time. Under the primary outage constraints and the peak power constraints at both ST and SR, to determine the average secondary throughput, we derive exact analytical expressions for the secondary outage probability and the ergodic capacity, which characterize the delay-limited and the delay-tolerant transmissions, respectively. We also investigate the effects of the number of primary transceivers and the peak power constraints on the optimal energy harvesting time that maximizes the secondary throughput. By utilizing the primary interference as an energy source, the secondary network achieves a better throughput performance compared to the case where the primary interference is ignored for energy harvesting purpose. Finally, we consider a case where ST also harvests energy from primary transmissions and compare its throughput performance with that of the non-energy harvesting ST case.
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We integrate a wireless powered communication network with a cooperative cognitive radio network,... more We integrate a wireless powered communication network with a cooperative cognitive radio network, where multiple secondary users (SUs) powered wirelessly by a hybrid access point (HAP) help a primary user relay the data. As a reward for the cooperation, the secondary network gains the spectrum access where SUs transmit to HAP using time division multiple access. To maximize the sum-throughput of SUs, we present a secondary sum-throughput optimal resource allocation (STORA) scheme. Under the constraint of meeting target primary rate, the STORA scheme chooses the optimal set of relaying SUs and jointly performs the time and energy allocation for SUs. Specifically, by exploiting the structure of the optimal solution, we find the order in which SUs are prioritized to relay primary data. Since the STORA scheme focuses on the sum-throughput, it becomes inconsiderate towards individual SU throughput, resulting in low fairness. To enhance fairness, we investigate three resource allocation schemes, which are (i) equal time allocation, (ii) minimum throughput maximization, and (iii) proportional time allocation. Simulation results reveal the trade-off between sum-throughput and fairness. The minimum throughput maximization scheme is the fairest one as each SU gets the same throughput, but yields the least SU sum-throughput.
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—The broadcast nature of the wireless medium allows unintended users to eavesdrop the confidentia... more —The broadcast nature of the wireless medium allows unintended users to eavesdrop the confidential information transmission. In this regard, we investigate the problem of secure communication between a source and a destination via a wireless energy harvesting untrusted node which acts as a helper to relay the information; however, the source and destination nodes wish to keep the information confidential from the relay node. To realize the positive secrecy rate, we use destination-assisted jamming. Being an energy-starved node, the untrusted relay harvests energy from the received radio frequency signals, which include the source's information signal and the destination's jamming signal. Thus, we utilize the jamming signal efficiently by leveraging it as a useful energy source. At the relay, to enable energy harvesting and information processing, we adopt power splitting (PS) and time switching (TS) policies. To evaluate the secrecy performance of this proposed scenario, we derive analytical expressions for two important metrics, viz., the secrecy outage probability and the ergodic secrecy rate. The numerical analysis reveals the design insights into the effects of different system parameters like power splitting ratio, energy harvesting time, target secrecy rate, transmit signal-to-noise ratio (SNR), relay location, and energy conversion efficiency factor, on the secrecy performance. Specifically, the PS policy achieves better optimal secrecy outage probability and optimal ergodic secrecy rate than that of the TS policy at higher target secrecy rate and transmit SNR, respectively.
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To appear in Proc. IEEE GLOBECOM 2015
We consider a spectrum sharing scenario, where a secondary network coexists with a primary networ... more We consider a spectrum sharing scenario, where a secondary network coexists with a primary network of multiple transceivers. The secondary network consists of an energy-constrained decode-and-forward secondary relay which assists the communication between a secondary transmitter and a destination in the presence of the interference from multiple primary transmitters. The secondary relay harvests energy from the received radio-frequency signals, which include the information signal from the secondary transmitter and the primary interference. The harvested energy is then used to decode the secondary information and forward it to the secondary destination. At the relay, we adopt a time switching policy due to its simplicity that switches between the energy harvesting and information decoding over time. Specifically, we derive a closed-form expression for the secondary outage probability under the primary outage constraint and the peak power constraint at both secondary transmitter and relay. In addition, we investigate the effect of the number of primary transceivers on the optimal energy harvesting duration that minimizes the secondary outage probability. By utilizing the primary interference as a useful energy source in the energy harvesting phase, the secondary network achieves a better outage performance.
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IEICE Transactions on Communications, Aug 2015
This paper investigates the detection performance of an improved energy detector for a secondary ... more This paper investigates the detection performance of an improved energy detector for a secondary user with spatially correlated multiple antennas. In an improved energy detector, an arbitrary positive power operation p replaces the squaring operation in a conventional energy detector, and the optimum value of p that gives the best detection performance may be different from 2. Firstly, for a given value of p, we derive closed-form expressions for the probability of detection and the probability of false alarm when antennas at the secondary user are exponentially correlated. We then find the optimum value of p for two different detection criteria−maximizing the probability of detection for a target probability of false alarm, and minimizing the probability of false alarm for a target probability of detection. We show that the optimum p is strongly dependent on system parameters like number of antennas, antenna correlation coefficient among multiple antennas, and average received signal-to-noise ratio (SNR). From results, we infer that, in low SNR regime, the effect of antenna correlation is less pronounced on the optimum p. Finally, we find the optimum values of p and threshold jointly that minimize the total error rate.
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To appear in Proc. of IEEE GLOBECOM 2015
Energy harvesting (EH) cognitive relays are an exciting solution to the problem of inefficient us... more Energy harvesting (EH) cognitive relays are an exciting solution to the problem of inefficient use of spectrum while achieving green communications and spatial diversity. In a spectrum sharing scenario, we investigate the performance of a cognitive relay network, where a secondary source communicates with its destination over Nakagami-$m$ channels via decode-and-forward EH relays while maintaining the outage probability of the primary user below a predefined threshold. Specifically, we derive a closed-form expression for the secondary outage probability and show that it is a function of the probability of an EH relay having sufficient energy for relaying, which in turn, depends on the energy harvesting and consumption rates of the EH relay and the primary outage probability threshold. We also show that relaxing the primary outage constraint may not always benefit the cognitive EH relay network due to the limitations imposed on the relay's transmit power by the energy constraint.
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To appear in Proc. of IEEE PIMRC 2015
This paper considers the cooperation between primary
and secondary users at information and ener... more This paper considers the cooperation between primary
and secondary users at information and energy levels when
both users are energy harvesting nodes. In particular, a secondary transmitter helps relaying the primary message, and in turn, gains the spectrum access as a reward. Also, the primary transmitter supplies energy to the secondary transmitter if the latter is energy-constrained, which facilitates an uninterrupted cooperation. We address this two-level cooperation over a finite horizon with the finite battery constraint at the secondary transmitter. While promising the rate-guaranteed service to both primary and secondary users, we aim to maximize the primary rate. We develop an iterative algorithm that obtains the optimal offline power policies for primary and secondary users. To acquire insights about the structure of the optimal solution, we examine specific scenarios. Furthermore, we investigate the effects of the secondary rate constraint and finite battery on the primary rate and the probability of cooperation. We show that the joint information and energy cooperation increases the chances of cooperation and achieves significant rate gains over only information cooperation.
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This letter analyzes the sensing-throughput tradeoff
for a secondary user (SU) under random arriv... more This letter analyzes the sensing-throughput tradeoff
for a secondary user (SU) under random arrivals and departures
of multiple primary users (PUs). We first study the case where
PUs change their status only during SU’s sensing period. We then
generalize to a case where PUs change status anytime during SU
frame, and compare the latter case with the former in terms of
the optimal sensing time and SU throughput. We also investigate
the effects of PU traffic parameters and the number of PUs on
the sensing-throughput tradeoff for SU. Results show that, though
the increase in the number of PUs reduces the optimal sensing
time for SU, the opportunity to find a vacant PU channel reduces
simultaneously, in turn, reducing SU throughput. Finally, we validate
the analysis by Monte Carlo simulations.
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To appear in Proceedings of 21st National Conference on Communications (NCC'15), Feb 2015
The use of cognitive relays is an emerging and promising solution to overcome the problem of spec... more The use of cognitive relays is an emerging and promising solution to overcome the problem of spectrum underutilization while achieving the spatial diversity. In this paper, we perform an outage analysis of the secondary system with amplify-and-forward relays in a spectrum sharing scenario, where a secondary transmitter communicates with a secondary destination over a direct link as well as the best relay. Specifically, under the peak power constraint, we derive a closed-form expression of the secondary outage probability provided that the primary outage probability remains below a predefined value. We also take into account the effect of primary interference on the secondary outage performance. Finally, we validate the analysis by simulation results.
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IEEE Communications Letters, Jul 2014
An energy harvesting cognitive radio scenario is considered where a secondary user (SU) with fini... more An energy harvesting cognitive radio scenario is considered where a secondary user (SU) with finite battery capacity opportunistically accesses the primary user (PU) channels. The objective is to maximize the throughput of SU under energy neutrality constraint and fading channel conditions in a single-user multi-channel setting. Channel selection criterion based on the probabilistic availability of energy with SU, channel conditions, and primary network’s belief state is proposed, which chooses the best subset of channels for sensing, yielding higher throughput. We construct channel-aware optimal and myopic sensing strategies in a Partially Observable Markov Decision Process framework based on the proposed channel selection criterion. The effects of sensing errors and collisions between PU and SU on the throughput of latter are studied. It is shown that there exists a trade-off between the transmission duration and the energy lost in collisions.
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in 10th International Conference on Signal Processing and Communications, Jul 2014
The effect of the primary traffic on a secondary user’s (SU) throughput under Rayleigh flat fadin... more The effect of the primary traffic on a secondary user’s (SU) throughput under Rayleigh flat fading channel is investigated. For this case, closed form expressions are derived for the average probability of detection and the average probability of false alarm. Based on these expressions, the average SU throughput under the desired signal-to-noise ratio (SNR) constraint in order to maintain the quality of the secondary link is found analytically considering the random arrival or departure of the primary user. It is shown that the spectrum sensing performance and SU throughput degrade with increase in the primary traffic and the deep fade condition of the channel over which the detection is performed. The degree of degradation in SU throughput is seen to be severed further due to the interference link from the primary transmitter to the secondary receiver. Under these detrimental effects, a sensing-throughput trade-off for SU is illustrated. Finally, the combined effect of the primary traffic, fading, imperfect spectrum sensing and the interference link from a primary transmitter is studied on the outage probability at SU.
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In Proceedings of 79th IEEE Vehicular Technology Conference-Spring (VTC-Spring), May 2014
"Block outlier detection methods, based on Tietjen-Moore (TM) and Shapiro-Wilk (SW) tests, are pr... more "Block outlier detection methods, based on Tietjen-Moore (TM) and Shapiro-Wilk (SW) tests, are proposed to detect and suppress spectrum sensing data falsification (SSDF) attacks by malicious users in cooperative spectrum sensing. First, we consider basic and statistical SSDF attacks, where the malicious users attack independently. Then we propose a new SSDF attack, which involves cooperation among malicious users by masking. In practice, the number of malicious users is unknown. Thus, it is necessary to estimate the number of malicious users, which is found using clustering and largest gap method. However, we show using Monte Carlo simulations that, these methods fail to estimate the exact number of malicious users when they cooperate. To overcome this, we propose a modified largest gap method."
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In Proceedings of 19th Asia-Pacific Conference on Communications, Aug 2013
Energy detection (ED) is a popular spectrum sensing technique in cognitive radio to detect the pr... more Energy detection (ED) is a popular spectrum sensing technique in cognitive radio to detect the primary user. But the detection performance of ED deteriorates in the presence of noise uncertainty and exhibits associated SNR wall phenomenon. In
this paper, the generalized energy detector (GED) is investigated,
where the squaring operation of amplitude of received samples in
conventional energy detector (CED) is replaced by an arbitrary
positive operation p. Our aim is to study the effect of noise
uncertainty on the detection performance of GED. We consider
different distributions of noise uncertainty. Initially, uniform
distribution of noise uncertainty is considered and an expression
of the SNR wall for the same is derived. It is shown that the SNR
wall for uniformly distributed noise uncertainty is independent
of p. The study of the detection performance of GED is further
extended for log-normally distributed noise uncertainty, where
the SNR wall is calculated numerically.
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In proceedings of 18th National Conference on Communications (NCC), IIT Delhi, Feb. 2013., Feb 2013
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Special Issue on Communication Systems and Image Processing Technology, Defence Science Journal, Jan 2013
In this paper, we focus on cooperative spectrum sensing (CSS) for double threshold improved energ... more In this paper, we focus on cooperative spectrum sensing (CSS) for double threshold improved energy detector. In this method, the improved energy detector compares positive power operation p of the amplitude of received signals at each secondary user (SU) with two thresholds to make binary decision about presence or absence of primary user (PU). The energies lying between upper and lower threshold are considered unreliable and are not considered in cooperation. The decisions are forwarded over an imperfect reporting channel to a fusion center where final decision on presence or absence of PU is taken. We combine double threshold approach with improved energy detection. Two step optimization is performed where cooperative probability of detection is maximized as a function of threshold difference in double threshold and then highest value of maximized cooperative probability of detection is found as a function of power operation p, average signal-to-noise ratio at SUs, number of cooperating SUs and cooperative probability of false alarm. Also, we find the optimum fusion rule at fusion center along with optimum power corresponding p to the lowest value of the minimized total error rate using two step optimization. Then we analyse the effect of errors introduced in reported decisions due to imperfect reporting channel.
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In proceedings of 18th National Conference on Communications (NCC), IIT Kharagpur, Feb. 2012., Feb 2012
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iitk.ac.in
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Drafts by Sanket Kalamkar
We address a fundamental question in wireless networks that, surprisingly, has not been studied b... more We address a fundamental question in wireless networks that, surprisingly, has not been studied before: what is the maximum density of concurrently active links that satisfy a certain outage constraint? We call this quantity the spatial outage capacity (SOC), give a rigorous definition, and analyze it for Poisson bipolar networks with ALOHA. Specifically, we provide exact analytical and approximate expressions for the density of links satisfying an outage constraint and give simple upper and lower bounds on the SOC. In the high-reliability regime where the target outage probability is close to zero, we obtain an exact closed-form expression of the SOC, which reveals the interesting and perhaps counter-intuitive result that all transmitters need to be always active to achieve the SOC, i.e., the transmit probability needs to be set to 1 to achieve the SOC.
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Papers by Sanket Kalamkar
and secondary users at information and energy levels when
both users are energy harvesting nodes. In particular, a secondary transmitter helps relaying the primary message, and in turn, gains the spectrum access as a reward. Also, the primary transmitter supplies energy to the secondary transmitter if the latter is energy-constrained, which facilitates an uninterrupted cooperation. We address this two-level cooperation over a finite horizon with the finite battery constraint at the secondary transmitter. While promising the rate-guaranteed service to both primary and secondary users, we aim to maximize the primary rate. We develop an iterative algorithm that obtains the optimal offline power policies for primary and secondary users. To acquire insights about the structure of the optimal solution, we examine specific scenarios. Furthermore, we investigate the effects of the secondary rate constraint and finite battery on the primary rate and the probability of cooperation. We show that the joint information and energy cooperation increases the chances of cooperation and achieves significant rate gains over only information cooperation.
for a secondary user (SU) under random arrivals and departures
of multiple primary users (PUs). We first study the case where
PUs change their status only during SU’s sensing period. We then
generalize to a case where PUs change status anytime during SU
frame, and compare the latter case with the former in terms of
the optimal sensing time and SU throughput. We also investigate
the effects of PU traffic parameters and the number of PUs on
the sensing-throughput tradeoff for SU. Results show that, though
the increase in the number of PUs reduces the optimal sensing
time for SU, the opportunity to find a vacant PU channel reduces
simultaneously, in turn, reducing SU throughput. Finally, we validate
the analysis by Monte Carlo simulations.
this paper, the generalized energy detector (GED) is investigated,
where the squaring operation of amplitude of received samples in
conventional energy detector (CED) is replaced by an arbitrary
positive operation p. Our aim is to study the effect of noise
uncertainty on the detection performance of GED. We consider
different distributions of noise uncertainty. Initially, uniform
distribution of noise uncertainty is considered and an expression
of the SNR wall for the same is derived. It is shown that the SNR
wall for uniformly distributed noise uncertainty is independent
of p. The study of the detection performance of GED is further
extended for log-normally distributed noise uncertainty, where
the SNR wall is calculated numerically.
Drafts by Sanket Kalamkar
and secondary users at information and energy levels when
both users are energy harvesting nodes. In particular, a secondary transmitter helps relaying the primary message, and in turn, gains the spectrum access as a reward. Also, the primary transmitter supplies energy to the secondary transmitter if the latter is energy-constrained, which facilitates an uninterrupted cooperation. We address this two-level cooperation over a finite horizon with the finite battery constraint at the secondary transmitter. While promising the rate-guaranteed service to both primary and secondary users, we aim to maximize the primary rate. We develop an iterative algorithm that obtains the optimal offline power policies for primary and secondary users. To acquire insights about the structure of the optimal solution, we examine specific scenarios. Furthermore, we investigate the effects of the secondary rate constraint and finite battery on the primary rate and the probability of cooperation. We show that the joint information and energy cooperation increases the chances of cooperation and achieves significant rate gains over only information cooperation.
for a secondary user (SU) under random arrivals and departures
of multiple primary users (PUs). We first study the case where
PUs change their status only during SU’s sensing period. We then
generalize to a case where PUs change status anytime during SU
frame, and compare the latter case with the former in terms of
the optimal sensing time and SU throughput. We also investigate
the effects of PU traffic parameters and the number of PUs on
the sensing-throughput tradeoff for SU. Results show that, though
the increase in the number of PUs reduces the optimal sensing
time for SU, the opportunity to find a vacant PU channel reduces
simultaneously, in turn, reducing SU throughput. Finally, we validate
the analysis by Monte Carlo simulations.
this paper, the generalized energy detector (GED) is investigated,
where the squaring operation of amplitude of received samples in
conventional energy detector (CED) is replaced by an arbitrary
positive operation p. Our aim is to study the effect of noise
uncertainty on the detection performance of GED. We consider
different distributions of noise uncertainty. Initially, uniform
distribution of noise uncertainty is considered and an expression
of the SNR wall for the same is derived. It is shown that the SNR
wall for uniformly distributed noise uncertainty is independent
of p. The study of the detection performance of GED is further
extended for log-normally distributed noise uncertainty, where
the SNR wall is calculated numerically.