• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.11
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• pp.4291-4310
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• 2015

This paper investigates the traffic offloading over unlicensed bands for two-tier multi-mode small cell networks. We formulate this problem as a Stackelberg game and apply a hierarchical learning framework to jointly maximize the utilities of both macro base station (MBS) and small base stations (SBSs). During the learning process, the MBS behaves as a leader and the SBSs are followers. A pricing mechanism is adopt by MBS and the price information is broadcasted to all SBSs by MBS firstly, then each SBS competes with other SBSs and takes its best response strategies to appropriately allocate the traffic load in licensed and unlicensed band in the sequel, taking the traffic flow payment charged by MBS into consideration. Then, we present a hierarchical Q-learning algorithm (HQL) to discover the Stackelberg equilibrium. Additionally, if some extra information can be obtained via feedback, we propose an improved hierarchical Q-learning algorithm (IHQL) to speed up the SBSs' learning process. Last but not the least, the convergence performance of the proposed two algorithms is analyzed. Numerical experiments are presented to validate the proposed schemes and show the effectiveness.

• Journal of dental hygiene science
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• v.7 no.3
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• pp.113-119
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• 2007

This study attempts to find factors contributing to the use pattern of prosthetics by investigating the current condition of prosthetics for the aged of over 65 years old by place of practice. Among those of over 65 years old who live in Gangnam-gu, Seocho-gu, Seongbuk-gu, and Gwanak-gu of Seoul and use the apartment senior's center, those having prosthetics were selected as subjects of this study, and this study was conducted in forms of interview and record. Findings of this study are summarized as follows: First, in regard of the state of prosthetics and relevant symptoms in the mouth according to the place of prosthetics practice, there was significant difference in the questions except the medical benefit of prosthetics between unlicensed facilities and dental clinics and hospitals. Second, regarding difference in satisfaction according to the place of prosthetics practice, dental clinics and hospitals showed a higher level of aesthetic satisfaction than unlicensed facilities. For difference in satisfaction at pronunciation, chewing, pain, a sense of foreign body, and holding power, dental clinics and hospitals showed a higher level than unlicensed facilities, Third, after factor analysis on the perception factors of unlicensed treatment and dental treatment, unlicensed facilities showed the highest level of reliability, and then convenience, word of mouth, and modernity in order. Dental clinics and hospitals also showed the highest level of reliability, however, and then convenience, modernity, and word of mouth in order. Fourth, as a consequence of analyzing the factors to influence the use pattern of prosthetics, regarding residential pattern, there were higher possibilities to use dental clinics and hospitals when the subjects lived together with their children and in Gangnam, and the more were the number of pyeong for the residence, pocket money, medical expense, and property in their name, compared to unlicensed facilities. In conclusion, economic factors appear to be the most important factors in selecting facilities for denture prosthodontics. Therefore, it is important to ensure the denture prosthodontics for the elderly are reimbursable so that they can enjoy a healthier life.

• ETRI Journal
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• v.42 no.1
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• pp.36-45
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• 2020

A priority-based data communication approach, developed by employing cognitive radio capacity for sensor nodes in a wireless terrestrial sensor network (TSN), has been proposed. Data sensed by a sensor node-an unlicensed user-were prioritized, taking sensed data importance into account. For data of equal priority, a first come first serve algorithm was used. Non-preemptive priority scheduling was adopted, in order not to interrupt any ongoing transmissions. Licensed users used a nonpersistent, slotted, carrier sense multiple access (CSMA) technique, while unlicensed sensor nodes used a nonpersistent CSMA technique for lossless data transmission, in an energy-restricted, TSN environment. Depending on the analytical model, the proposed wireless TSN environment was simulated using Riverbed software, and to analyze sensor network performance, delay, energy, and throughput parameters were examined. Evaluating the proposed approach showed that the average delay for sensed, high priority data was significantly reduced, indicating that maximum throughput had been achieved using wireless sensor nodes with cognitive radio capacity.

• Journal of Korea Society of Digital Industry and Information Management
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• v.7 no.3
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• pp.75-83
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• 2011

Cognitive radio (CR) technology is to maximize the spectrum utilization by allocating the unused spectrums to the unlicensed users. This technology enables the sharing of channels among secondary (unlicensed) and primary (licensed) users on a non-interference basis after sensing the vacant channel and as a result, it is possible to harness wireless frequency more efficiently. To enhance the accuracy of sensing, RDSS was suggested. It is a fusion mechanism based on the reputation of sensing nodes and WSPRT (weighted sequential probability ratio test). However, in RDSS, the execution number of WSPRT could increase according to the order of inputted sensing values, and the fast defense against the forged values is difficult. In this paper, we propose a transaction signing-based authentication scheme for secure distributed spectrum sensing to response the forged values. The validity of proposed scheme is provided by BAN logic.

• TTA Journal
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• s.155
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• pp.93-100
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• 2014

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.79-86
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• 2015

Cognitive radio networks (CRNs) offer the promise of intelligent radios that can learn from and adapt to their environment. CRN permits unlicensed users to utilize the idle spectrum as long as it does not introduce interference to the primary users due to the Federal Communications Commission's recent regulatory policies. Thereby, the security aspects in CRNs should be different with the other networks. The purpose of this paper is to devise a new delegation-based authentication protocol (NDAP) by extracting out the security aspects for unlicensed user authentication over CRNs from Tsai et al's delegation-based authentication protocol (TDAP). First of all, we will provide security analyses on the TDAP and set design goal for unlicensed user authentication. Then, we will propose a NDAP as a remedy mechanism for the TDAP and a new protocol for CRNs. The NDAP could be used as a security building block for the CRNs and various convergence applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.6
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• pp.589-592
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• 2015

In this paper, we suggested a real-time test-bed for analyzing frequency interference between 2.4 GHz unlicensed devices, such as WiFi, Zigbee, etc. Owing to versatile programming capability of Universal Software Radio Peripheral(USRP) and $Labview^{TM}$, frequency interference environments can be easily modeled. Therefore, performance degradation effects due to various parameters of interferer and victim receiver can be analyzed intuitively. For verification, we showed a frequency interference scenario, which consists of IEEE 802.15.4 as a victim and IEEE 802.11b as a interferer. Measured Bit Error Rate(BER) results showed good agreement with theory and simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.208-211
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• 2016

Device-to-Device communication(D2D) enables devices in proximity to communicate directly without going through the network infrastructure. In particular, D2D communications in a cellular network can improve the spectral efficiency by allowing the reuse of cellular resources. However, it is not easy to maintain the channel quality of the D2D links and to protect the cellular links from the D2D interferences, since the resource allocations for the cellular users will change with time due to the time-varying nature of the cellular channels. To mitigate the performance degradation of D2D links, we propose to exploit unlicensed bands as auxiliary resources when the D2D links share the uplink cellular resources. The effectiveness of the proposed scheme is verified through simulations.

• Journal of IKEEE
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• v.23 no.1
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• pp.91-98
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• 2019

LTE's extension for unlicensed spectrum called Licensed Assisted Access (LAA) is equipped with Listen-Before-Talk (LBT) designed similar with the backoff mechanism of Wi-Fi for coexistence. However, Wi-Fi's backoff mechanism has not evolved from its old design for compatibility with legacy devices, thus LAA's LBT is not efficient either in utilizing spectrum. If LAA operates with no Wi-Fi systems in proximity, it can run more efficient LBT. In this paper, we propose Narrowband Clear Channel Assessment (NCCA) for narrowband transmission. In NCCA, an LAA node performs LBT in either wide or each narrow bandwidth segment. This allows multiple LAA nodes to perform simultaneous transmissions in orthogonal bandwidth segments in the same time slot. We design four variants of NCCA implementation and model their performance using a mathematical model. The coexistence performance of NCCA with conventional wideband nodes and the accuracy of the model are shown via simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.8
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• pp.1074-1081
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• 2021

It has recently been noticed that the headway of unlicensed wireless technology is necessary as user's demands of wireless tech increase and the development of high-speed data service by using low-power short-range wireless network is needed. Hence, it is inevitable to study sharing and coexistence for broadband spectrum of diverse unlicensed application with wide bandwidth. In this paper, an interference examination between unlicensed WiFi (Wireless Fidelity) in the 6GHz and OB (Outside Broadcasting) system which is an incumbent service in the same frequency band was conducted and it suggests separation distance for the coexistence. Thus, MCL (Minimum Coupling Loss) and MC (Monte Carlo) methods were used to set up interference scenarios for the interference analysis and compute the separation distance between two systems according to the same frequency band and frequency separation.