• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.129-129
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• 2009

In this paper, a tunable microstrip patch antenna designed using RF MEMS switches is reported. The design and simulation antenna were performed using high frequency structure simulator (HFSS). The antenna was designed in ISM Band and operates simultaneously at 2.4 GHz and 5.7 GHz with a -10 dB return-loss bandwidth of 20 MHz and 180 MHz, respect-tively. To obtain high efficiency and improve integrated ability, the High Resistivity Silicon (HRS) wafer was used for the antenna. The antenna achieved high gain with 8 dB at 5.7 GHzand 1.5 dB at 2.4 GHz. The RF MEMS DC contact switches was simulated and analysis by ANSYS software.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.110-116
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• 2012

This paper proposes a new diversity antenna which is the base of MIMO, tunable and reconfigurable antennas. The antenna has a small size and high inter-antenna isolation resulting from the compact radiating element comprising a meandered line and an open-loop combined in one limited uniplanar space and a modified T-shaped decoupling structure, respectively. In a WiMAX band, the radiating element and the entire antenna are $0.092{\lambda}$ and $0.2216{\lambda}$ in size, which shows effective size-reduction and the gain and efficiency of the proposed antenna attached to the ground of a handheld device are 3.7dBi and 56% acceptable to the industrial standard.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.8
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• pp.880-885
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• 2010

In this paper, we propose a reconfigurable beam steering antenna using a dipole and a loop. The radiation patterns of the two antennas were cancelled or compensated, and head for the specific direction when a dipole and a loop antenna are combined at the reasonable ratio. The structure of the antenna is very simple and planar. By changing on/ off states of switches, the proposed antenna can steer the beam direction in the x-y plane. Simulation results confirmed the steering characteristic by using two imaginary switches. The proposed antenna can change the direction of the maximum gain in the x-y plane($0^{\circ}$, ${\pm}50^{\circ}$). The proposed antenna operates in 2.5~2.56 GHz(VSWR<2). It showed that peak gain of the antenna is 1.96~2.48 dBi and overall beam width of the reconfigurable antenna covers about $125^{\circ}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1327-1336
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• 2007

In this paper, we propose a reconfigurable antenna which operates as a disk-loaded dipole antenna and a folded dipole antenna alternatively using RF on/off switches. The antenna can change its effective length to achieve dual-band operation; operates as the folded dipole antenna for stepping up the radiation resistance in low frequency band of $20{\sim}300$ MHz, and as the disk-loaded dipole antenna for an omni-directional radiation pattern (horizontal plane) and a donut-shaped radiation pattern (vertical plane) in high frequency band of $300{\sim}1.3$ GHz. In the low band, the proposed antenna shows higher gain than a conventional dipole antenna with a reduced antenna size. In the high band, the antenna maintains a broad beamwidth of about $80^{\circ}$, thus the antenna can be applicable to antennas for direction finding applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1159-1165
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• 2008

In this paper, a single-feed equilateral-triangular microstrip antenna with truncated corners is used for achieving diverse radiation polarization. The proposed antenna is excited by a microstrip line, which is place parallel to an oblique side of the equilateral-triangular patch. Depending on whether the three identically-sized comers of the triangular patch are cut or not, the equilateral-triangular microstrip antenna shows linear polarization(LP) or left-hand circular polarization(LHCP) or Tight-hand circular polarization(RHCP). Based on the equilateral-triangular microstrip antenna with truncated corners, a novel reconfigurable microstrip antenna with switchable polarization sense is also proposed. The proposed reconfigurable antenna has a simple structure, consisting of a corner-truncated triangular patch, a small triangular conductor, and a microstrip line. Using a biased PIN diode between the patch and the small triangular conductor, it can produce LP or RHCP according to bias voltages. From the measured results, low cross polarization level when operated in the linear state and good axial ratio in the circular state are observed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.11
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• pp.77-84
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• 2003

This paper presents a multi-functional microstrip spital antenna that operates in dual frequency bands. Several types of beam shape can be selected by controlling the phase difference of two spiral arms with the phase shifters located on each feed line. It has a normal beam at the lower frequency band, and four different patterns at the higher frequency band: normal beam, conical beam and two types of tilted beam. The antenna exhibits more than 10% of bandwidth at each band. The antenna is fabricated with conductor backed electromagnetic absorber in order to attain unidirectional radiation pattern and confirmed the multi-functionality by measurements.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.46-52
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• 2010

A compact circular microstrip patch antenna with a switchable circular polarization(CP) is proposed at 2.4 GHz. An unequal cross-shaped slot on a ground plane is utilized as a perturbation. By switching pin diodes mounted on the slot, the CP sense of each antenna can be simply switched from left-handed(LH) CP to right-handed(RH) CP vice versa. Since the perturbation can be made on the ground plane and no bias circuit is required on the patch side, the bias circuit has not effect on the main beam radiation. From the experimental results, the impedance bandwidth and CP bandwidth of the proposed antenna have shown up to 150 MHz and 35 MHz, respectively. The peak gain of the proposed antenna is 1.7 dBi for both CP senses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4125-4130
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• 2015

This paper presents the communication performance for the radiation pattern reconfigurable antenna in the wearable device measuring bio signal (temperature, blood pressure, pulse etc.) of human body. The operational frequency is 2.4 - 2.5 GHz, which covers Bluetooth communication bandwidth. The maximum gain of the antennas is 1.96 dBi. The proposed antenna is efficiently transmitting and receiving signal by generating two opposite beam directions using two RF switches (PIN diode). Also, we investigated how radiation pattern changes according to three angles ($30^{\circ}$, $90^{\circ}$, $150^{\circ}$) of Top Loading. In this paper, we measured and compared the SNR (Signal-to-Noise Ratio) and BER (Bit Error Rate) performances of the proposed antennas in the condition between an ideal environment of anechoic chamber and smart house existing practical electromagnetic interferences (Universal Software Radio Peripheral, USRP). Throughout the comparing the results of the measurement of two cases, we found that the SNR is degraded over 5dB in average and BER is increased over ten times in maximum, therefore, it is confirmed that the error rate of receiving signal is increased. The measured results of SNR and BER value in this paper able to expect the performance degrading by the interference from the electromagnetic devices.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.33-48
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• 2018

In this paper, we characterise the joint interference alignment and power allocation strategies for a K-user multicell multiple-input multiple-output (MIMO) Gaussian interference channel. We consider a MIMO interference channel with a blind interference alignment through staggered antenna switching on the receiver. We explore the power allocation and the feasibility condition for cooperative cell-edge (CE) mobile users (MUs) by assuming that the channel state information is unknown. The new insight behind the transmission strategy of the proposed scheme is premeditated (randomly generated transmission strategy) and partial cooperative CE MUs, where the transmitter is equipped with a conventional antenna, the receiver is equipped with a reconfigurable multimode antenna (staggered antenna switching pattern), and the receiver switches between preset T modes. Our proposed scheme assists and aligns the desired and interference signals to cancel the common interference signals, since the received signal must have a corresponding independent signal subspace. The sum capacity for a K-user multicell MIMO Gaussian interference channel with reconfigurable multimode antennas is completely characterised.