• Journal of the Optical Society of Korea
• /
• v.12 no.4
• /
• pp.346-350
• /
• 2008

In this paper, we analyze the performance of a reliable, scalable, and cost-effective switchless wavelength division multiplexing (WDM) network based on an arrayed waveguide grating (AWG). The network efficiency is significantly increased by spatially reusing wavelengths and exploiting multiple free spectral ranges (FSRs) of the AWG employed in the architecture. We have analyzed the performance of this architecture by simulating in $Optsim^{TM}$ with a control channel which exploits the broadband light source, i.e., an LED. The data was successfully transmitted to a distance of 30 km without using any EDFA's in the network, with a reasonable BER of $4.0530{\times}10^{-14}$. We have analyzed the performance of this architecture with a control channel which exploits the broadband light source, i.e., an LED, by simulating in $Optsim^{TM}$.

• ETRI Journal
• /
• v.44 no.6
• /
• pp.925-935
• /
• 2022

In this study, we propose a limited feedback-based frequency divided group beamforming with sparse space-frequency transmit diversity coded orthogonal frequency division multiplexing (OFDM) system for ultrareliable low latency communication (URLLC) scenario. The proposed scheme has several advantages over the traditional hybrid beamforming approach, including not requiring downlink channel state information for baseband precoding, supporting distributed multipoint transmission structures for diversity, and reducing beam sweeping latency with little uplink overhead. These are all positive aspects of physical layer characteristics intended for URLLC. It is suggested in the system to manage the multipoint transmission structure realized by distributed panels using a power allocation method based on cooperative game theory. Link-level simulations demonstrate that the proposed scheme offers reliability by achieving both higher diversity order and array gain in a nonline-of-sight channel of selectivity and limited spatial scattering.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.1A
• /
• pp.8-18
• /
• 2011

Visible light communication (VLC) using optical sources which can be simultaneously utilized for illumination and communication is currently an attractive option for wireless personal area network. Improving the data rate in optical wireless communication system is challenging due to the limited bandwidth of the optical sources. In this paper, we design the singular value decomposition (SVD)-based multiplexing multi-input multi-output (MIMO) system to support two data streams in optical wireless channels. In order to improve the spectral efficiency, the rate adaptation using multi-level pulse amplitude modulation (PAM) is applied according to the channel condition and we propose the method to allocate the optical power, the offset and the size of modulation scheme theoretically under the constraints of the nonnegativity of the modulated signals, the aggregate optical power and the bit error rate (BER) requirement. The simulation results show that the proposed allocation method gives the better performance than the method to allocate the optical power equally for each data stream.

• Korean Journal of Optics and Photonics
• /
• v.22 no.6
• /
• pp.276-282
• /
• 2011

We performed experiments on Hong-Ou-Mandel type two-photon interference with frequency entangled photon pairs at 1.5 ${\mu}m$ telecommunication band generated through femtosecond pulsed spontaneous parametric down-conversion. Two different angular frequencies ${\omega}_1$ and ${\omega}_2$ were selected using CWDM(coarse wavelength division multiplexing) filters at the output ports of the interferometer. The coincidence counting rates were measured with varying path-length difference between the two interferometer arms to observe the two-photon interference patterns of spatial beating. The obtained visibilities in the net coincidence were close to the theoretical limit of 100%.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.8A
• /
• pp.592-599
• /
• 2009

In this paper, we consider multiuser multi-input/multi-output antenna systems with zero-forcing receivers in downlink. In this case, to exploit multiuser diversity, spatial-division multiple access (SDMA) system allows to assign different users to a part of transmit antennas at the base station whereas spatial-division multiplexing (SDM) system assigns all antennas to single user's data stream. In this paper, we present analytical frameworks to evaluate performance of these systems. We first analyze the performance of these two systems by deriving closed-form expressions of achievable throughput. Numerical results show that the derived expressions are very tight. In addition, we approximate the capacity expression of SDM and SDMA systems and compare the SDM with the optimal case.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.19 no.5
• /
• pp.506-514
• /
• 2008

At coverage boundaries of cellular systems including the recent WiBro standard which operate with full frequency reuse for increased spectral efficiency, interference signals from the base stations(BS) of adjacent cells degrade the receiver performance. In this paper, a detection method for multiple-antenna mobile stations(MS) is proposed for downlink performance improvement at coverage boundaries of cellular systems. For the performance verification, we obtain the probability density function(pdf) of the effective signal-to-interference and noise ratio(SINR) according to the variation of the interference signals from adjacent cells as well as the number of MS antennas, and calculate the transmission efficiency. We also verify the performance of proposed method with simulation results, to demonstrate a significant performance improvement is achieved over the maximal ratio combining(MRC) and spatial demultiplexing(SD) methods in terms of the effective SINR and the spectral efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.2C
• /
• pp.95-112
• /
• 2007

Spatial Multiplexing techniques, which is a kind of Multiple antenna techniques, provide high data transmission rate by transmitting independent data at different transmit antenna with the same spectral resource. OFDM (Orthogonal Frequency Division Multiplexing) is applied to MIMO (Multiple-Input Multiple-Output) system to combat ISI (Inter-Symbol Interference) and frequency selective fading channel, which degrade MIMO system performance. But, orthogonality between subcarriers of OFDM can't be guaranteed under high-mobility condition. As a result, severe performance degradation due to ICI is induced. In this paper, both ICI and CAI (Co-Antenna Interference) which occurs due to correlation between multiple antennas, and performance degradation due to both ICI and CAI are analyzed. In addition to the proposed CIR (Channel Impulse Response) estimation method for avoiding loss in data transmission rate, HIC (Hybrid Interference Cancellation) approach for guaranteeing QoS of MIMO-OFDM receiver is proposed. We observe the results on analytical performance degradation due to both ICI & CAI are coincide with the simulation results and performance improvement due to HIC are also verified by simulation under SCM-E Sub-urban Macro MIMO channel.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.5
• /
• pp.25-32
• /
• 2007

This paper proposes a distributed space-frequency block code (SFBC) for relay-assisted single carrier frequency-domain equalization (SC-FDE). The proposed technique achieves spatial diversity gain over fast fading channels without the complexity of multiple antennas. The mobile equipment of the proposed system has a very simple transmitter structure with constant amplitude transmit sequences, which is desirable especially for uplink communications. In order to obtain spatial diversity, the transmit sequence of relay is efficiently generated in the time domain, which is equivalent to the SFBC. Further, efficient implementation of relay and destination structures is also presented. Extensive simulation results show that the proposed system significantly outperforms the distributed space-time block code (D-STBC) SC-FDE over fast fading channels.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.5C
• /
• pp.351-360
• /
• 2008

In cellular mobile radio systems with frequency reuse, the interference signals degrade the channel estimation and signal detection performance due to the low signal-to-interference ratio near coverage boundaries. When the preamble pilot sequences from different cells are orthogonal or located in disjointed positions, they can be used for multi-cell channel estimation and interference cancellation. In time-varying channels caused by Doppler spread, data pilot symbols are needed for channel estimations. However, data pilot symbols are usually located in identical positions for the overhead reduction, which degrades the channel estimation performance. In this paper, we demonstrate a significant amount of performance improvement is achieved by multiplying different pseudonoise(PN) sequences to the data pilot symbols from adjacent interference cells. In particular, for detection scheme using maximal ratio combining(MRC) and inter-cell spatial demultiplexing(ISD), quantitative performance gain of spectral efficiency for different values of Doppler frequency and interference power is presented.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.2
• /
• pp.102-107
• /
• 2011

In multicell wireless systems with insufficient frequency reuse, user transmission will suffer other-cell interference (OCI). Cell cooperation is an effective way to mitigate OCI and increase the system sum rate. An adaptive scheme for serving one user in each cell was proposed in [1]. In this paper, we generalize that scheme by serving two users in each cell with adaptive zeroforcing beamforming (ZF) strategies. Based on our derived statistics of the signal-to-noise plus interference ratios, we choose the scheme to maximize the total ergodic sum-rate based on user locations. Through the numerical examples, we show that the total system sum rate can be improved by selecting appropriate transmitting strategy adaptively. As a result, our proposed system can explore spatial multiplexing gain without additional power and thus improves total system sum rate significantly.