• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.15 no.9
• /
• pp.1889-1894
• /
• 2011

Channel allocation is one of the important issues in the multichannel transmission. In the cognitive radio networks, channel allocation scheme should be designed to improve spectrum efficiency without interfering with the transmission of licensed users. In this paper, we propose a spectrum hole prediction based channel allocation scheme. The proposed channel allocation scheme, predicts spectrum hole by using the channel success rate, and limit the transmission of secondary user's data, and it reduces the interference to the primary user. The performance of proposed channel allocation scheme is evaluated by the computer simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.10
• /
• pp.4952-4975
• /
• 2018

An induced hesitant linguistic aggregation operator is investigated in the paper, in which, hesitant fuzzy linguistic evaluation values are associated with probabilistic information. To deal with these hesitant fuzzy linguistic information, an induced hesitant fuzzy linguistic probabilistic ordered weighted averaging (IHFLPOWA) operator is proposed, monotonicity, boundary and idempotency of IHFLPOWA are proved. Then andness, orness and the entropy of dispersion of IHFLPOWA are analyzed, which are used to characterize the weighting vector of the operator, these properties show that IHFLPOWA is extensions of the induced linguistic ordered weighted averaging operator and linguistic probabilistic aggregation operator. In this paper, IHFLPOWA is utilized to gather linguistic information and create fuzzy ontologies, and a movie fuzzy ontology as an illustrative case study is used to show the elaboration of the proposed method and comparison with the existing linguistic aggregation operators, it seems that the IHFLPOWA operator is an useful and alternative operator for dealing with hesitant fuzzy linguistic information with probabilistic information.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.8C
• /
• pp.689-695
• /
• 2007

Wireline relay stations(RS's) are connected to cellular base stations(BS's) via radio-over-fiber(RoF) to enhance system capacity and to reduce shadow areas. Unlike wireless multi-hop systems, BS-to-RS signaling is transmitted out-of-band, thus reducing the effect of interference caused by frequency reuse. In this paper, antenna arrays used in addition to the wireline RS's are considered to evaluate the transmission capacity gain and performance variations according to the may structures. In particular, RS locations to maximize the gain, may distribution patterns for a given number of antenna elements, performance enhancement for a varying number of elements are experimentally determined to suggest a proper utilization of antenna ways in conjunction with wireline RS's.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.7
• /
• pp.3414-3434
• /
• 2016

Classical key generation is complicated to update and key distribution generally requires fixed infrastructures. In order to eliminate these restrictions researchers have focused much attention on physical-layer (PHY-layer) based key generation methods. In this paper, we present a PHY-layer fingerprints based fuzzy key generation scheme, which works to prevent primary user emulation (PUE) attacks and spectrum sensing data falsification (SSDF) attacks, with multi-node collaborative defense strategies. We also propose two algorithms, the EA algorithm and the TA algorithm, to defend against eavesdropping attacks and tampering attacks in mobile cognitive radio networks (CRNs). We give security analyses of these algorithms in both the spatial and temporal domains, and prove the upper bound of the entropy loss in theory. We present a simulation result based on a MIMO-OFDM communication system which shows that the channel response characteristics received by legitimates tend to be consistent and phase characteristics are much more robust for key generation in mobile CRNs. In addition, NIST statistical tests show that the generated key in our proposed approach is secure and reliable.

• Journal of Communications and Networks
• /
• v.13 no.4
• /
• pp.327-338
• /
• 2011

With the incitation to reduce power consumption and the aggressive reuse of spectral resources, there is an inevitable trend towards the deployment of small-cell networks by decomposing a traditional single-tier network into a multi-tier network with very high throughput per network area. However, this cell size reduction increases the complexity of network operation and the severity of cross-tier interference. In this paper, we consider a downlink two-tier network comprising of a multiple-antenna macrocell base station and a single femtocell access point, each serving multiples users with a single antenna. In this scenario, we treat the following beamforming optimization problems: i) Total transmit power minimization problem; ii) mean-square error balancing problem; and iii) interference power minimization problem. In the presence of perfect channel state information (CSI), we formulate the optimization algorithms in a centralized manner and determine the optimal beamformers using standard convex optimization techniques. In addition, we propose semi-decentralized algorithms to overcome the drawback of centralized design by introducing the signal-to-leakage plus noise ratio criteria. Taking into account imperfect CSI for both centralized and semi-decentralized approaches, we also propose robust algorithms tailored by the worst-case design to mitigate the effect of channel uncertainty. Finally, numerical results are presented to validate our proposed algorithms.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.349-353
• /
• 2015

We use multi-wavelength observations of galaxy groups to probe the formation models for galaxy formation in cosmological simulations, statistically. The observations include Chandra and XMM-Newton X-ray observations, optical photometry and radio observations at 1.4 GHz and 610 MHz. Using a large sample of galaxy groups observed by the XMM-Newton X-ray telescope as part of the XMM-Large Scale Survey, we carried out a statistical study of the redshift evolution of the luminosity gap for a well defined mass-selected group sample and show the relative success of some of the semi-analytic models in reproducing the observed properties of galaxy groups up to redshift z ~ 1.2. The observed trend argues in favour of a stronger evolution of the feedback from active galactic nuclei at z < 1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the luminosity gap does not evolve with redshift and is well reproduced by the models. We find that the radio power of giant elliptic galaxies residing in galaxy groups with a large luminosity gap are lower compared to giant ellipticals of the same stellar masses but in typical galaxy groups.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.4
• /
• pp.335-341
• /
• 2016

In this paper, we propose the method of controling the turns of a receiving coil for the matching directly to the receiver input impedance(typically $50{\Omega}$) with a maximum wireless power transfer(WPT) efficiency. Based on the presented the expression of the optimum load depending on a system figure of merit, number of the turns of a receiving coil, and proximity effect between conducting lines, the theoretical efficiencies have been compared with the measured ones with a good agreement. The results of this work may be used to realize a allowable maximum efficiency with a simple and low-profile 2-coil WPT system not requiring a separate feeding loop.

• Journal of Communications and Networks
• /
• v.13 no.5
• /
• pp.456-462
• /
• 2011

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.2
• /
• pp.353-368
• /
• 2023

The four wing unmanned aerial vehicle owns the characteristics of small size, light weight, convenient operation and well stability. But it is easily disturbed by external environmental factors during flight with these disadvantages of short endurance and poor attitude solving ability. For solving these problems, a microprocessor based on STM32 chip is designed and the overall development is completed by the resources such as built-in timer and multi-function mode general-purpose input/output provided by the master micro controller unit, together with radio receiver, attitude meter, barometer, electronic speed control and other devices. The unmanned aerial vehicle can be remotely controlled and send radio waves to its corresponding receiver, control the analog level change of its corresponding channel pins. The master control chip can analyze and process the data to send multiple sets pulse signals of pulse width modulation to each electronic speed control. Then the electronic speed control will transform different pulse signals into different sizes of current value to drive the motor located in each direction of the frame to generate different rotational speed and generate lift force. To control the body of the unmanned aerial vehicle, so as to achieve the operator's requirements for attitude control, the PID controller based on Kalman filter is used to achieve quick response time and control accuracy. Test results show that the design is feasible.

• ETRI Journal
• /
• v.45 no.1
• /
• pp.28-44
• /
• 2023

We propose short packet communication in an underlay cognitive radio network assisted by an intelligent reflecting surface (IRS) composed of multiple reconfigurable reflectors. This scheme, called the IRS protocol, operates in only one time slot (TS) using the IRS. The IRS adjusts its phases to give zero received cumulative phase at the secondary destination, thereby enhancing the end-to-end signal-to-noise ratio. The transmitting power of the secondary source is optimized to simultaneously satisfy the multi-interference constraints, hardware limitations, and performance improvement. Simulation and analysis results of the average block error rates (BLERs) show that the performance can be enhanced by installing more reconfigurable reflectors, increasing the blocklength, lowering the number of required primary receivers, or sending fewer information bits. Moreover, the proposed IRS protocol always outperforms underlay relaying protocols using two TSs for data transmission, and achieves the best average BLER at identical transmission distances between the secondary source and secondary destination. The theoretical analyses are confirmed by Monte Carlo simulations.