END-TO-END THROUGHPUT MAXIMIZATION FOR UNDERLAY MULTI-HOP COGNITIVE RADIO NETWORKS WITH RF ENERGY HARVESTING
ABSTRACT
This paper studies a green paradigm for the underlaycoexistence of primary users (PUs) and secondary users(SUs) in energy harvesting cognitive radio networks (EH-CRNs),wherein battery-free SUs capture both the spectrum and theenergy of PUs to enhance spectrum efficiency and green energyutilization. To lower the transmit powers of SUs, we employmulti-hop transmission with time division multiple access, bywhich SUs first harvest energy from the RF signals of PUs andthen transmit data in the allocated time concurrently with PUs,all in the licensed spectrum. In this way, the available transmitenergy of each SU mainly depends on the harvested energy beforethe turn to transmit, namely energy causality. Meanwhile, thetransmit powers of SUs must be strictly controlled to protect PUsfrom harmful interference. Thus, subject to the energy causalityconstraint and the interference power constraint, we study theend-to-end throughput maximization problem for optimal timeand power allocation. To solve this nonconvex problem, we firstequivalently transform it into a convex optimization problemand then propose the joint optimal time and power allocation(JOTPA) algorithm that iteratively solves a series of feasibilityproblems until convergence. Extensive simulations evaluate theperformance of EH-CRNs with JOTPA in three typical deploymentscenarios and validate the superiority of JOTPA by makingcomparisons with two other resource allocation algorithms.
PROPOSED SYSTEM:
The major contributions of this paper can be summarizedas follows:_ First, different from conventional CRNs that take PT asinterference or even ignore PT for simplicity, this paperregards PT as a friend that provides both spectrum andenergy for SUs. In doing so, we investigate a novel greencoexistence paradigm to enhance spectrum efficiency andgreen energy utilization. Moreover, this paradigm can beregarded as another type of SWIPT where PR is theinformation receiver and SUs are the energy receivers._ Second, subject to the energy causality constraint andthe interference power constraint, we study the endto-endthroughput maximization problem with respectto time and power allocation, and propose the JOTPAalgorithm to obtain the optimal solution. To the best ofour knowledge, the optimal resource allocation for theend-to-end throughput maximization of underlay multihopEN-CRNs has not been studied before._ Third, by moving the EH-CRN around PUs, we investigatethree typical scenarios to show how the deploymentsof EH-CRN influence the performance, which can guideus to deploy the EH-CRN properly. Moreover, to validatethe superiority of the proposed algorithm, we compareJOTPA with OTEPA and ETOPA, and demonstrate thatJOTPA gains larger end-to-end throughput and highergreen energy utilization than OTEPA and ETOPA underall considered scenarios.
EXISTING SYSTEM:
To exploit the spectrum and the energy of PUs, SUs inEH-CRNs can operate in three kinds of paradigms, namely,interweave, overlay and underlay.In interweave paradigms, SUs first harvest energy and thenopportunistically access the licensed spectrum when PUs aredetected as inactive. In, spectrum sensing is optimizedto maximize the throughput when SUs harvest energy fromambient energy sources. Then, a two-dimensional spectrumand power sensing scheme is proposed for the case that bothPUs and SUs harvest energy from the same renewable source. Furthermore, a spectrum access scheme is proposed forthroughput maximization in, in which SUs harvest energyfrom the active PUs. In, throughput and outage probabilityare derived for the case that SUs opportunistically harvestenergy from the nearby PUs.In overlay paradigms, SUs consume energy to serve bothPUs and SUs provided that there are excellent cooperationsbetween PUs and SUs. In, throughput maximizationis studied for the case that one SU harvests energy from ambientRF signals, serves as the relay for PUs, and communicateswith another SU. After extending one SU to multiple SUs,relay selection to maximize throughput or sum-throughputis investigated in, wherein SUs harvest energyfrom PUs or a hybrid access point (H-AP). In, sumthroughputmaximization is studied for overlay EH-CRNs,wherein a H-AP first performs WET for multiple SUs aswell as information transmission for PUs, and then collectsdata from SUs. Similarly, energy efficiency maximization isstudied in, wherein uplink scheduling and cooperativepower control are considered.
CONCLUSION
In this paper, we formulated a green coexistence paradigmfor underlay multi-hop EH-CRNs, in which battery-free SUscapture both the spectrum and the energy of PUs to enhancespectrum efficiency and green energy utilization. With thisparadigm, we investigated the end-to-end throughput maximizationproblem subject to the energy causality constraintand the interference power constraint, and proposed the JOTPAalgorithm to achieve optimal resource allocation. By movingthe multi-hop EH-CRNs around PUs, we observed thatdeploying the former SUs close to PUs can achieve largerend-to-end throughput and higher green energy utilizationthan deploying the latter SUs close to PUs. Moreover, bymaking comparisons a three different resource allocationalgorithms, we concluded that JOTPA obtains larger endto-endthroughput and higher green energy utilization thanETOPA and OTEPA under all considered scenarios.This paper provides a lower-bound for the performance ofmulti-hop EH-CRNs in underlay paradigm, as energy storageand management are inapplicable for the battery-free SUs.Future works considering energy storage and managementwill further improve the performance. Furthermore, it will benecessary to study advanced energy management schemes tocope with the dynamics of PUs if the multi-hop EH-CRNswork in interweave, overlay or even hybrid paradigm
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