• Journal of Broadcast Engineering
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• v.24 no.7
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• pp.1221-1227
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• 2019

This paper describes a low-density parity-check (LDPC) coded index modulated orthogonal frequency division multiplexing with quasi-orthogonal sequence (IM-OFDM-QOS) and provides performance evaluations of the proposed system. By using QOS as the spreading code, IM-OFDM-QOS scheme can improve the reception performance than IM-OFDM-SS scheme for a given data rate. On the other hand, LDPC code is widely used to the latest wireless communication systems as forward error correction (FEC) scheme and has Shannon-limit approaching performance. Therefore, by applying LDPC code to IM-OFDM-QOS system as FEC scheme, the reception performance can be further improved. Simulation results show that significant signal-to-noise ratio (SNR) gains can be obtained for LDPC coded IM-OFDM-QOS system compared to the LDPC coded IM-OFDM-SS system and the SNR gain increases with the higher code rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.229-237
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• 2010

The conventional detection methods developed for spatially-multiplexed MIMO systems such as OSIC and QRD-M show performance difference for each user depending on the order of detection when they are applied to detection of multi-user signals in uplink multiuser systems based on collaborative spatial multiplexing. In this paper, a signal detection method for uplink multiuser systems based on collaborative spatial multiplexing is proposed to provide similar performance for each user while its performance is close to the case of ML detection. Compared with QRD-M method, computational complexity of the proposed signal detection method is similar in the case of QPSK, and significantly lower in the case of high modulation order with 16-QAM and 64-QAM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.8 no.4
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• pp.164-171
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• 1983

In this paper, angular division multiplexing of the optical multiplexing technique for transmitting several channels using a relatively short step-index fiber is described. Mode coupling and the output power distributionin the fiber for the plane wave excitations is calculated and the crosstalk level determination of the system is proposed. In the presence of the mode coupling, the pulse width in terms of the fiber's length and input condition is calculated in the slab waveguide and the fiber. For the input angles (

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.44-49
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• 2008

Recently, a so called orthogonal spatial multiplexing(OSM) scheme was presented which allows simple maximum likelihood decoding at the receiver with single phase feedback In this paper, by serially concatenating this scheme by a linear precoder, a new closed-loop SM scheme is proposed for two transmit arid two receive antennas. By computer simulation results, we show that the proposed scheme outperforms the conventional SM and OSM. For the proposed code, we also propose a new simple decoding algorithm which leads to a greatly reduced decoding complexity compared with the ML receiver without any loss of error performance.

• Journal of Broadcast Engineering
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• v.13 no.5
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• pp.677-680
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• 2008

In this paper, a new orthogonal frequency division multiplexing (OFDM) with 3-dimensional (3-D) signal mapper is proposed. Here, the signal mapper consists of signals on the surface of Poincare sphere. If the signal points are uniformly distributed and normalized to have the same average power, the minimum Euclidean distance of a 3-D constellation is much larger than that of a 2-D constellation. Computer simulation shows that the proposed OFDM has much improved error performance as compared with the conventional system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.5
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• pp.806-808
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• 2015

In this paper, we suggest the method of pilot tone design for a compressed channel sensing in order to decrease the peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.471-480
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• 2013

The beating of two or more lasers that have the same or a finite difference in the central frequencies, is the main source of noise in spectral amplitude coding optical code division multiple access (SAC OCDMA) systems. In this paper we adopt a spatial multiplexing (SM) scheme for SAC OCDMA systems to mitigate this beat noise. The results show that for different code weights and different data rates SM SAC can support a larger number of users than the conventional SAC for all different laser source configurations. However, SM SAC requires a more complex system than the conventional SAC, and almost twice as much optical component.

• Journal of Korea Multimedia Society
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• v.24 no.8
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• pp.1012-1019
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• 2021

Currently, since the black-white QR (Quick Response) codes have limited storage capacity, color QR codes have been actively being studied. By multiplexing 3 colors, the color QR codes can allow the code capacity to be increased by three times, however, the color multiplexing brings about the possibility of crosstalk and noises in the acquisition process of the final image, incurring the decrease of bit-recognition rate. In order to improve the bit recognition rate, while keeping the storage capacity high, this paper proposes a new type of color QR code which uses the pattern information as well as the color information, and then analyzes how to increase the bit recognition rate. For this aim, the paper presents an efficient system which extracts embedded information from color QR code and then, through practical experiments, it is shown that the proposed color QR codes improves the bit recognition rate and are useful for commercial applications, compared to the conventional color codes.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2847-2851
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• 2020

A simple water level measurement method based on wavelength division multiplexing (WDM) is proposed and demonstrated. The measurement principle is based on the change of Fresnel reflection occurring at the end facet of the optical fiber tip (OFT). To increase the spatial resolution of water level sensing, a broadband light source (BLS) and an arrayed waveguide grating (AWG) are employed. The OFTs are multiplexed with the dedicated wavelength channels of AWG. By measuring all of the reflection powers reflected at the OFTs with a proposed on-site reflectometer, the water level can be monitored continuously for a fast emergency response. Moreover, it can be implemented easily with the commercially available optical components and devices with the simple configuration.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.138-141
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• 2002

광굴절 결정체가 홀로그래픽 저장 매개체로 이용될 수 있음이 Chen에 의해 제시된 이후, 광굴절 결정체는 대용량 광메모리로서 관심의 초점이 되었다. 그리하여 홀로그래픽 기법을 이용하여 이미지를 광굴절 결정체에 저장시키는 방법에 대한 연구가 광범위하게 이루어져 왔다. 보통 여러개의 홀로그램을 저장 매체인 광굴절 결정체에 중첩하여 저장하는 경우, 먼저 기록된 홀로그램이 뒤이어 기록되는 홀로그램들에 의해서 지워지기 때문에 먼저 기록된 홀로그램의 복원이 어려워진다. (중략)