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Relaying protocols for wireless energy harvesting and information processing
 IEEE Trans. Wireless Commun
, 2013
"... An emerging solution for prolonging the lifetime of energy constrained relay nodes in wireless networks is to avail the ambient radiofrequency (RF) signal and to simultaneously harvest energy and process information. In this paper, an amplifyandforward (AF) relaying network is considered, where a ..."
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Cited by 58 (7 self)
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An emerging solution for prolonging the lifetime of energy constrained relay nodes in wireless networks is to avail the ambient radiofrequency (RF) signal and to simultaneously harvest energy and process information. In this paper, an amplifyandforward (AF) relaying network is considered, where an energy constrained relay node harvests energy from the received RF signal and uses that harvested energy to forward the source information to the destination. Based on the time switching and power splitting receiver architectures, two relaying protocols, namely, i) time switchingbased relaying (TSR) protocol and ii) power splittingbased relaying (PSR) protocol are proposed to enable energy harvesting and information processing at the relay. In order to determine the throughput, analytical expressions for the outage probability and the ergodic capacity are derived for delaylimited and delaytolerant transmission modes, respectively. The numerical analysis provides practical insights into the effect of various system parameters, such as energy harvesting time, power splitting ratio, source transmission rate, source to relay distance, noise power, and energy harvesting efficiency, on the performance of wireless energy harvesting and information processing using AF relay nodes. In particular, the TSR protocol outperforms the PSR protocol in terms of throughput at relatively low signaltonoiseratios and high transmission rate. Index Terms Energy harvesting, wireless energy transfer, amplifyandforward, cooperative systems, throughput, outage
Stability analysis and power optimization for energy harvesting cooperative networks
 IEEE Signal Process. Lett
, 2012
"... Abstract—In this letter, we investigate the effects of networklayer cooperation in a wireless threenode network with energyharvesting nodes and bursty data traffic. By modelling energy harvesting in each node as a queue (buffer) that stores the received energy, we study the interaction between d ..."
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Cited by 24 (5 self)
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Abstract—In this letter, we investigate the effects of networklayer cooperation in a wireless threenode network with energyharvesting nodes and bursty data traffic. By modelling energy harvesting in each node as a queue (buffer) that stores the received energy, we study the interaction between data and energy queues when only knowledge of the arrival rates is available. The maximum stable throughput (in packets/slot) of the source as well as the required transmitted power for both a noncooperative and an orthogonal decodeandforward cooperative schemes are derived in closedform. We prove that cooperation achieves a higher maximum stable throughout than direct link for scenarios with poor energy arrival rates. Index Terms—Cooperative networks, energy harvesting, power optimization, stable throughput. I.
Relay selection for simultaneous information transmission and wireless energy transfer: A tradeoff perspective,” Available online at arXiv:1303.1647
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Wireless information and power transfer with full duplex relaying
 IEEE Trans. Commun
, 2014
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Competitive ratio analysis of online algorithms in energy harvesting communication system
, 2011
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Generalizing the amplifyandforward relay gain model: An optimal SEP perspective,” Submitted to
 Proceedings of the 2012 IEEE ICCS
"... Abstract—Two models for AF relaying, namely, fixed gain and fixed power relaying, have been extensively studied in the literature given their ability to harness spatial diversity. In fixed gain relaying, the relay gain is fixed but its transmit power varies as a function of the sourcerelay channel ..."
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Abstract—Two models for AF relaying, namely, fixed gain and fixed power relaying, have been extensively studied in the literature given their ability to harness spatial diversity. In fixed gain relaying, the relay gain is fixed but its transmit power varies as a function of the sourcerelay channel gain. In fixed power relaying, the relay transmit power is fixed, but its gain varies. We revisit and generalize the fundamental twohop AF relaying model. We present an optimal scheme in which an average power constrained AF relay adapts its gain and transmit power to minimize the symbol error probability (SEP) at the destination. Also derived are insightful and practically amenable closedform bounds for the optimal relay gain. We then analyze the SEP of MPSK, derive tight bounds for it, and characterize the diversity order for Rayleigh fading. Also derived is an SEP approximation that is accurate to within 0.1 dB. Extensive results show that the scheme yields significant energy savings of 2.07.7 dB at the source and relay. Optimal relay placement for the proposed scheme is also characterized, and is different from fixed gain or power relaying. Generalizations to MQAM and other fading distributions are also discussed. Index Terms—Cooperative systems, spatial diversity, relays, MPSK, MQAM, power constraint, modulation, fading channels, amplifyandforward, symbol error probability, relay placement.
Performance Analysis of Fixed Gain AmplifyandForward Relaying with TimeEfficient Cascaded Channel Estimation
"... Abstract—In a cooperative system with an amplifyandforward relay, the cascaded channel training protocol enables the destination to estimate the sourcedestination channel gain and the product of the sourcerelay (SR) and relaydestination (RD) channel gains using only two pilot transmissions from ..."
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Abstract—In a cooperative system with an amplifyandforward relay, the cascaded channel training protocol enables the destination to estimate the sourcedestination channel gain and the product of the sourcerelay (SR) and relaydestination (RD) channel gains using only two pilot transmissions from the source. Notably, the destination does not require a separate estimate of the SR channel. We develop a new expression for the symbol error probability (SEP) of AF relaying when imperfect channel state information (CSI) is acquired using the above training protocol. A tight SEP upper bound is also derived; it shows that full diversity is achieved, albeit at a high signaltonoise ratio (SNR). Our analysis uses fewer simplifying assumptions, and leads to expressions that are accurate even at low SNRs and are different from those in the literature. For instance, it does not approximate the estimate of the product of SR and RD channel gains by the product of the estimates of the SR and RD channel gains. We show that cascaded channel estimation often outperforms a channel estimation protocol that incurs a greater training overhead by forwarding a quantized estimate of the SR channel gain to the destination. The extent of pilot power boosting, if allowed, that is required to improve performance is also quantified. I.
Wireless information and power transfer in relay systems with multiple antennas and interference
 IEEE Trans. Commun., vol: PP
"... Abstract—In this paper, an energy harvesting dualhop relaying system without/with the presence of cochannel interference (CCI) is investigated. Specifically, the energy constrained multiantenna relay node is powered by either the information signal of the source or via the signal receiving from b ..."
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Cited by 2 (2 self)
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Abstract—In this paper, an energy harvesting dualhop relaying system without/with the presence of cochannel interference (CCI) is investigated. Specifically, the energy constrained multiantenna relay node is powered by either the information signal of the source or via the signal receiving from both the source and interferer. In particular, we first study the outage probability and ergodic capacity of an interference free system, and then extend the analysis to an interfering environment. To exploit the benefit of multiple antennas, three different linear processing schemes are investigated, namely, 1) Maximum ratio combining/maximum ratio transmission (MRC/MRT), 2) Zeroforcing/MRT (ZF/MRT) and 3) Minimum meansquare error/MRT (MMSE/MRT). For all schemes, both the systems outage probability and ergodic capacity are studied, and the achievable diversity order is also presented. In addition, the optimal power splitting ratio minimizing the outage
The Diversity Potential of Relay Selection with Practical Channel Estimation
"... Abstract—We investigate the diversity order of decodeandforward relay selection in Nakagamim fading, in cases where practical channel estimation techniques are applied. In this respect, we introduce a unified model for the imperfect channel estimates, where the effects of noise, timevarying chan ..."
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Abstract—We investigate the diversity order of decodeandforward relay selection in Nakagamim fading, in cases where practical channel estimation techniques are applied. In this respect, we introduce a unified model for the imperfect channel estimates, where the effects of noise, timevarying channels, and feedback delays are jointly considered. Based on this model, the correlation between the actual and the estimated channel values, ρ, is expressed as a function of the signaltonoise ratio (SNR), yielding closedform expressions for the overall outage probability as a function of ρ. The resulting diversity order and power gain reveal a high dependence of the performance of relay selection on the high SNR behavior of ρ, thus shedding light onto the effect of channel estimation on the overall performance. It is shown that when the channel estimates are not frequently updated in applications involving timevarying channels, or when the amount of power allocated for channel estimation is not sufficiently high, the diversity potential of relay selection is severely degraded. In short, the main contribution of this paper lies in answering the following question: How fast should ρ tend to one, as the SNR tends to infinity, so that relay selection does not experience any diversity loss? Index Terms—Relay selection, imperfect channel estimation, Nakagamim fading model. I.
Relaying and Stability in Energy Harvesting Simple Networks
"... AbstractWireless systems of rechargeable nodes have extended lifetime and are selfsufficient. The transmission policies in these systems need to adapt to the harvested energy availability. In this work, we investigate the interaction between relaying, energy harvesting, and stability. We introduc ..."
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AbstractWireless systems of rechargeable nodes have extended lifetime and are selfsufficient. The transmission policies in these systems need to adapt to the harvested energy availability. In this work, we investigate the interaction between relaying, energy harvesting, and stability. We introduce the problem of general relaying cost minimization for cooperative energy harvesting networks. We consider a simple network in which a source transmits to a destination through networklevel cooperation with a number of relay nodes. The source and the relays have energy harvesting capability. To adapt the relaying process to the available harvested energy, we exploit partial relay cooperation in which the flows through the relays are controlled. The relaying cost minimization problem is feasible when the data queues of the source and the relays are stable. The stability conditions of the data queues are derived. Then, we introduce the energy consumption as a cost criterion for the optimization problem to find an energyefficient partial relaying protocol. We assess the effect of partial relay cooperation compared to the cases of no cooperation and full relay cooperation.