• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.512-519
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• 2016

This paper presents spectrum utilization strategies in cognitive radio (CR) networks powered by multi-antenna based wireless energy transfer. Secondary access point (AP) with multiple antennas should transfer the energy to the secondary sensor nodes with energy beamforming and simultaneously induces no interference to PUs. In addition, sensor nodes can transmit information to the secondary AP using the harvested energy, only when the spectrum is not utilized by PUs. We analyze the achievable rate of the CR sensor networks and propose an interference nulling energy beamforming method to maximize the achievable rate. Finally, we also propose a frame scheduling algorithm in which the durations of wireless energy transfer/information transfer frames (phases) are optimized.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.291-303
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• 2006

In this paper, we analyze functional requirements of the IEEE 802.22 WRAN, and propose a downlink 프레임 structure satisfying the requirements. The proposed downlink 프레임 structure maximizes e transmission efficiency by adopting the cognative radio to assign the sub-channel by reflecting the channel environment of WRAN. We also calculate the signalling overhead for both downlink and uplink, and analyze the performances of time synchronization, frequency synchronization and cell identification based on the 프리앰블 in downlink and suggest the channel estimation method tough 프리앰블 or pilot. As a final result, e stationary beamforming (SBF) algorithm with dynamic channel allocation(DCA) is proposed. The proposed OFDMA downlink 프레임 structure with channel adaptive sub-channel allocation for cognitive radio applications is verified to meet the requirements of IEEE 802.22 WRAN, by computer simulations.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.6
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• pp.812-819
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• 2012

Interference and jamming are becoming increasing concern to a radar system nowdays. AESA(Active Electronically Steered Array) antennas and adaptive beamforming(ABF), in which antenna beam patterns can be modified to reject the interference, offer a potential solution to overcome the problems encountered. In this paper, we've developed a planar active phased array radar system, in which ABF, target detection and tracking algorithm operate in real-time. For the high output power and the low noise figure of the antenna, we've designed the S-band TRMs based on GaN HEMT. For real-time processing, we've used wavelenth division multiplexing technique on fiber optic communication which enables rapid data communication between the antenna and the signal processor. Also, we've implemented the HW and SW architecture of Real-time Signal Processor(RSP) for adaptive beamforming that uses SMI(Sample Matrix Inversion) technique based on MVDR(Minimum Variance Distortionless Response). The performance of this radar system has been verified by near-field and far-field tests.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.4
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• pp.530-536
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• 1993

In adaptive antenna, recently Gooch suggested a new adaptive system using equation error method, but the system demands inverse model about the pole part and thus does not guarantee stability. In this paper, algorithm is proposed that has a basis on Popov's extra-stability theory. And system is developed of output error method. In addition, the result obtained by applying proposed algorithm to system of output error method is compared with that of Gooch model.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2E
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• pp.40-43
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• 2004

In moving jammer environments, the performance of conventional adaptive beamformer is severely degraded and the robust adaptive beamformer requires additional sensors to obtain desired performances. Therefore, it is necessary to develop efficient algorithm without any additional requirement of the number of sensors, etc. In this paper, we introduce a fast adaptive algorithm with variable forgetting factor, which does not have any additional requirements. From the computer simulations, we obtain the better performances than those of other techniques for the arrays with various aperture lengths.

• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.430-436
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• 2007

In this paper, we assume the uplink multiuser MIMO system based on FDD. Considering the implementation of practical system, Antenna selection and Transmit Beamforming scheme are suggested. System model of both two schemes are introduced and the scheduling algorithm which approaches the optimal performance with affordable computational complexity is proposed for each transmission scheme. Simulation results show that the sum-rate of the proposed low complexity scheduler approaches the performance of brute-force scheduler which is believed to be the optimal scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.32-35
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• 2018

Massive multiple-input multiple-output (MIMO) transmission is an essential technique for achieving the high bandwidth efficiency required in 5G mobile communication systems. Various forms of arrays can be used as the number of antenna elements increases for massive MIMO transmission. In this letter, we propose a beamforming algorithm applicable to multiuser MIMO transmission using uniform circular arrays. By employing quasi-orthogonal beam pairs obtained from the inter-beam correlation information, we minimize inter-user interference and evaluate the resulting performance gain.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.53-60
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• 2013

In this paper, the new multi-beamforming is proposed for Multiple-input multiple-output (MIMO) Multicarrier-Code division multiple access(MC-CDMA) systems to overcome the decrease of performance due to multiuser interference and multiple-antenna interference. Installing the number of multi-beamformer which is equal to the number of multi-transmitter antennas and exploiting the proposed approach at the receiver of MIMO MC-CDMA, the multi-beams are formed toward each multi-antenna of desired user and null beam are formed to other interference. Therefore, the performance of MIMO MC-CDMA system is improved as removing the interference signal. BER performance improvement is investigated through computer simulation by the proposed approach to MIMO MC-CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1469-1476
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• 2015

We propose a beam selection algorithm that improves inter sector SIR using a code-book of a circular array antenna in multi-sector wireless mesh network environments. The proposed method improves SIR using a combination of fed back code-book and guarantees QoS of all nodes. Computer simulation exhibits the proposed scheme demonstrates 4.42dB higher SIR than that of the conventional code-book method, QoS with proportional fair is improved by 1.70dB and fact that all nodes are satisfied Qos is also shown.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.12
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• pp.5212-5230
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• 2016

How to determine the right number of small base stations to activate in multi-cell uplinks to match traffic from a fixed quantity of K users is an open question. This paper analyses the uplink cooperative that jointly receives base stations activation to explore this question. This paper is different from existing works only consider transmitting power as optimization objective function. The global objective function is formulated as a summation of two terms: transmitting power for data and coordinated overhead for control. Then, the joint base stations activation and beamforming problem is formulated as a mixed integer second order cone optimization. To solve this problem, we develop two polynomial-time distributed methods. Method one is a two-stage solution which activates no more than K small base stations (SBSs). Method two is a heuristic algorithm by dual decomposition to MI-SOCP that activates more SBSs to obtain multiple-antennae diversity gains. Thanks to the parallel computation for each node, our methods are more computationally efficient. The strengths and weaknesses of these two proposed two algorithms are also compared using numerical results.