• Journal of Communications and Networks
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• v.13 no.4
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• pp.360-366
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• 2011

In this paper, we investigate the problem of power allocation in a heterogeneous network that is composed of a pair of cognitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to characterize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situations is introduced to protect the primary network from unacceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the combined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the proposed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.

• Journal of Environmental Science International
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• v.30 no.5
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• pp.369-378
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• 2021

In this study, we investigated the effects of indole on biofilm formation inhibition in Pantoea agglomerans (P. agglomerans). In the biofilm growth assay, indole inhibited biofilm formation across all the growth time. Depending on biofilm growth stage, indole exhibited biofilm inhibition and anti-bacterial effects on planktonic cells. Through the analysis of the proportion rate between biofilm and Colony Forming Units (CFU) and inhibition rate of indole, we confirmed that depending on the biofilm stage of P. agglomerans, indole treatment timing was more important than the treatment duration. By comparing gene expression rates through rt-qPCR P.agglomerans affected by indole was found to significantly change quorum sensing (pagI/R) and indole transportation (bssS) gene expressions. Throughout all, indole exhibited both antimicrobial and anti-biofilm effects on P. agglomerans. In addition, we confirmed the anti-biofilm effects of indole on mature biofilm. In conclusion, indole as a signal molecule, can exhibit anti-biofilm effects through bacterial quorum sensing inhibition and indole affects. Therefore, indole can regulate biofilm bacteria especially gram-negative opportunistic pathogens.

• Journal of Microbiology and Biotechnology
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• v.34 no.4
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• pp.795-803
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• 2024

Microorganisms usually coexist as a multifaceted polymicrobial community in the natural habitats and at mucosal sites of the human body. Two opportunistic human pathogens, Pseudomonas aeruginosa and Staphylococcus aureus commonly coexist in the bacterial infections for hospitalized and/or immunocompromised patients. Here, we observed that autolysis of the P. aeruginosa quorum-sensing (QS) mutant (lasRmvfR) was suppressed by the presence of the S. aureus cells in vitro. The QS mutant still displayed killing against S. aureus cells, suggesting the link between the S. aureus-killing activity and the autolysis suppression. Independent screens of the P. aeruginosa transposon mutants defective in the S. aureus-killing and the S. aureus transposon mutants devoid of the autolysis suppression revealed the genetic link between both phenotypes, suggesting that the iron-dependent metabolism involving S. aureus exoproteins might be central to both phenotypes. The autolysis was suppressed by iron treatment as well. These results suggest that the interaction between P. aeruginosa and S. aureus might be governed by mechanisms that necessitate the QS circuitry as well as the metabolism involving the extracellular iron resources during the polymicrobial infections in the human airway.

• Journal of Internet Computing and Services
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• v.12 no.4
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• pp.35-43
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• 2011

Cognitive Radio (CR) ad hoc network is highly considered as one of promising future ad hoc networks, which enables opportunistic access to under-utilized licensed spectrum. Similarly to other CR networks, the spectrum sensing is a prerequisite in CR ad hoc network. Collaborative spectrum sensing can help increasing sensing performance. For such an infrastructureless network, however the coordination for the sensing collaboration is really complicated due to the lack of a central controller. In this paper, we propose a novel collaborative spectrum sensing scheme in which the final decision is made by the node with the highest data reliability based on a sequential Dempster Shafer theory. The collaboration of sensing data is also executed by the proposed contention-aware reporting mechanism which utilizes the sensing data reliability order for broadcasting spectrum sensing result. The proposed method reduces the collecting time and the overhead of the control channel due to the efficiency of the ordered sequential combination while keeping the same sensing performance in comparison with the conventional cooperative centralized spectrum sensing scheme.

• International journal of advanced smart convergence
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• v.7 no.3
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• pp.23-36
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• 2018

In wireless communication, efficient spectrum usage is an issue that has been an attractive research area for many technologies. Recently new technologies innovations allow compact radios to transmit with power efficient communication over very long distances. For example, Low-Power Wide Area Networks (LPWANs) are an attractive emerging platform to connect the Internet-of-Things (IoT). Especially, LoRa is one of LPWAN technologies and considered as an infrastructure solution for IoT. End-devices use LoRa protocol across a single wireless hop to communicate to gateway(s) connected to the internet which acts as a bridge and relays message between these LoRa end-devices to a central network server. The use of the (ISM) spectrum sharing for such long-range networking motivates us to implement spectrum sensing testbed for cognitive radio network based on LoRa and GNU radio. In cognitive radio (CR), secondary users (SUs) are able to sense and use this information to opportunistically access the licensed spectrum band in absence of the primary users (PUs). In general, PUs have not been very receptive of the idea of opportunistic spectrum sharing. That is, CR will harmfully interfere with operations of PUs. Subsequently, there is a need for experimenting with different techniques in a real system. In this paper, we implemented spectrum sensing for cognitive radio networks based on LoRa and GNU Radio, and further analyzed corresponding performances of the implemented systems. The implementation is done using Microchip LoRa evolution kits, USRPs, and GNU radio.

• Proceedings of the Korean Society of Computer Information Conference
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• 2015.07a
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• pp.279-281
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• 2015

Location awareness is an important capability for mobile-based indoor services. Those indoor services have motivated the implementation of methods that need high computational load cost and complex mechanisms for positioning prediction. These mechanisms, such as opportunistic sensing and machine learning, require more energy consumption to achieve accuracy. In this paper, we propose the Bluetooth Low Energy indoor zone detection (BLEIZOD) technique. This method exploits the concept of proximity zone to reduce the load cost and complexity. Our proposed method implements the received signal strength indicator (RSSI) function more effectively to gain accuracy and reduce energy consumption.

• Annual Conference of KIPS
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• 2007.05a
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• pp.1288-1290
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• 2007

Congestion in WSN increases energy dissipation rates of sensor nodes as well as loss of packets and thereby hinders fair and reliable event detections. We find that one of the key reasons of congestion in WSN is allowing sensing nodes to transfer as many packets as possible. This is due to the use of CSMA/CA that gives opportunistic media access control. In this paper, we propose an energy efficient congestion avoidance protocol that includes source count based hierarchical and load adaptive medium access control. Our proposed mechanism ensures load adaptive media access to the nodes and thus achieves fairness in event detection. The results of simulation show our scheme exhibits more than 90% delivery ratio with retry limit 1, even under bursty traffic condition which is good enough for reliable event perception.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9A
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• pp.853-866
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• 2008

In this paper, a multi-hop relaying transmission scheme is analyzed regarding its feasibility and potentiality in the IEEE 802.22-based cognitive radio (CR) environment. Shortly, basic design issues are addressed such as relay station (RS) deployment and a frame structure of physical channel to escape inter-hop interference. This paper mainly develops a radio resource management scheme based on spectrum sensing results aggregated from CR secondary nodes and improves the opportunistic spectrum sharing efficiency. In particular, a decision rule about a channel availability is made using a distributed sensing method. Subsequently, spectrum allocation and routing path decision procedures are proposed to establish a link from source to destination with a hop-by-hop manner. Simulation results show that the proposed multi-hop relaying scheme is substantially profitable in CR environments if the number of hops and RS deployment are designed in such a way that the spectrum sharing gain is larger than spectrum division loss which is inherently induced in multi-hop relaying systems.

• Journal of Microbiology and Biotechnology
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• v.32 no.2
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• pp.220-227
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• 2022

The spread of antibiotic-resistant strains of Staphylococcus aureus, a gram-positive opportunistic pathogen, has increased due to the frequent use of antibiotics. Inhibition of the quorum-sensing systems of biofilm-producing strains using plant extracts represents an efficient approach for controlling infections. Torilis japonica is a medicinal herb showing various bioactivities; however, no studies have reported the anti-biofilm effects of T. japonica extracts against drug-resistant S. aureus. In this study, we evaluated the inhibitory effects of T. japonica ethanol extract (TJE) on biofilm production in methicillin-sensitive S. aureus (MSSA) KCTC 1927, methicillin-resistant S. aureus (MRSA) KCCM 40510, and MRSA KCCM 40511. Biofilm assays showed that TJE could inhibit biofilm formation in all strains. Furthermore, the hemolysis of sheep blood was found to be reduced when the strains were treated with TJE. The mRNA expression of agrA, sarA, icaA, hla, and RNAIII was evaluated using reverse transcription-polymerase chain reaction to determine the effect of TJE on the regulation of genes encoding quorum sensing-related virulence factors in MSSA and MRSA. The expression of hla reduced in a concentration-dependent manner upon treatment with TJE. Moreover, the expression levels of other genes were significantly reduced compared to those in the control group. In conclusion, TJE can suppress biofilm formation and virulence factor-related gene expression in MSSA and MRSA strains. The extract may therefore be used to develop treatments for infections caused by antibiotic-resistant S. aureus.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.6-10
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• 2015

RF energy harvesting technology is a promising technology for generating the electrical power from ambient RF signal to operate low-power consumption devices(eg. sensor) in wireless communication networks. This paper, motivated by this and building upon existing CR(Cognitive Radio) network model, proposes a optimal control policy for RF energy harvesting CR networks model where secondary users that have low power consumption harvest ambient RF energy from transmission by nearby active primary users, while periodically sensing and opportunistically accessing the licensed spectrum to the primary user's network. We consider that primary users and secondary users are distributed as Poisson point processes and contact with their intended receivers at fixed distances. Finally we can derive the optimal frame duration, transmission power and density of secondary user from the proposed model that can maximize the secondary users's throughput under the given several conditions and suggest future directions of research.