• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.1-7
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• 2000

Generally, one-dimensional fiber optic code-division multiple-access(CDMA) system is encoded and decoded using optical orthogonal codes(OOC’s), where two-dimensional fiber optic CDMA system uses optical orthogonal signature pattern codes(OOSPC’s) for parallel data link process. The OOSPC’s should have good autocorrelation and cross-correlation properties. However, if timing information or synchronization of OOSPC’s can be obtained by other means, the property of autocorrelation may not be restricted and we can increase the number of pattern codes. In this paper we introduce the fiber optic CDMA system for parallel transmission of two-dimensional data and investigate methods of generation of two-dimensional pattern codes. The probability density function of interference noise is calculated in interfering OOSPC’s of the users and the corresponding bit error rate is derived.. We compare each OOSPC’s by plotting bit error rate versus threshold values and the number of simultaneous users, from the result, we propose the optimal OOSPC’s conditions for the parallel transmission of two-dimensional data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7A
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• pp.964-972
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• 1999

In this paper, we proposed a simulation model to which apply the AAL 2 (AAL type 2) between BSC and MSC in the cellular mobile communication systems. We suggested the frame structure of processing the packets of short length and the scheme which multiplex to one or more ATM cell. Also, we analyzed the performance of the APR, transmission delay, and channel transmission efficiency used in the packetized voice traffic and the low bit-rate data traffic such as fax. From the simulation results, the maximum number of users are 47 users without using AAL 2 multiplexing, but the maximum number of users are 70 (Non-Overlapping scheme) users, 110 (Overlapping scheme) users, respectively. Thus, we knew that the Overlapping scheme is more efficient than the Non-Overlapping scheme. Finally, we showed that the optimum transmission buffer size is 4 ATM cells in the cellular communication systems with the bandwidth of 2 Mbps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.706-711
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• 2012

The current visible light communication (VLC) systems have a short transmission distance and a low data rate. To overcome this, we studied on the method of appling MIMO technology to VLC. However, it is difficult to apply the original MIMO technology used in RF frequency to wireless VLC. In VLC system, a lens can be used to separate the transmitted signals. And, if we use an image sensor as the receiver, MIMO technology can be applied to LED wireless visible light communication. In this paper, we report an experiment of $2{\times}2$ LED wireless visible light communication using a commercial image sensor receiver. We show the experimental demonstration with a transmission length of 10.5 m and a data rate of 200 bit/s.

• Journal of Broadcast Engineering
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• v.24 no.6
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• pp.1002-1012
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• 2019

360VR content requires short latency, such as immediate response to viewers' viewport changes and high quality video delivery. It is necessary to consider efficient transmission that guarantees the QoE(Quality of Experience) of the 360VR contents with limited bandwidth. Several research has been introduced to reduce overall bandwidth consumption by predicting a user's viewport and allocating different bit rates to the area corresponding to the viewport. In this paper, we propose novel viewport prediction scheme that uses sound source location information of 360VR contents as auditory recognition information along with visual recognition information. Also, we propose efficient transmission algorithm by allocating a bit rate properly based on improved viewport prediction. The proposed scheme improves the accuracy of the viewport prediction and provides high quality videos to tiles corresponding to the user's viewpoint within the limited bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5B
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• pp.448-456
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• 2003

In this parer, an ABR (Available Bit Rate) congestion control algorithm for voice transmission in ATM networks was proposed. To deal with the network congestion problem, not only the buffer level of a switch but also the variation of the buffer level were considered. Also, to resolve the unfairness among sources where the bit transfer rates vary, a loading factor that is used to adjust the bit rate was introduced. To show the superiority of this paper over others, simulation was done with a network of 7 voice sources and 4 switches, which was represented by Petri net model. ExSpect was used for simulation. The simulation results showed that there was improvement in network utilization and that unfairness among sources were resolved a lot.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.172-181
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• 2010

In this paper, we propose an adaptive block quantization method. The propose method perfrect reconstructs side information without high complexity in the encoder side, as transmitting motion vectors from a decoder to an encoder side. Also, at the encoder side, residual signals between reconstructed side information and original frame are adaptively quantized to minimize parity bits to be transmitted to the decoder. The proposed method can effectively allocate bits based on bit error rate of side information. Also, we can achieved bit-saving by transmission of parity bits based on the error correction ability of the LDPC channel decoder, because we can know bit error rate and positions of error bit in encoder side. Experimental results show that the proposed algorithm achieves bit-saving by around 66% and delay of feedback channel, compared with the convntional algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.7
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• pp.2998-3017
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• 2018

Massive (large-scale) MIMO (multiple-input multiple-output) is one of the key technologies in next-generation wireless communication systems. This paper proposes a high-performance low-complexity turbo receiver for SC-FDMA (single-carrier frequency-division multiple access) based MMIMO (massive MIMO) systems. Because SC-FDMA technology has the desirable characteristics of OFDMA (orthogonal frequency division multiple access) and the low PAPR (peak-to-average power ratio) of SC transmission schemes, the 3GPP LTE (long-term evolution) has adopted it as the uplink transmission to meet the demand high data rate and low error rate performance. The complexity of computing will be increased greatly in base station with massive MIMO (MMIMO) system. In this paper, a low-complexity adaptive turbo equalization receiver based on normalized minimal symbol-error-rate for MMIMO SC-FDMA system is proposed. The proposed receiver is with low complexity than that of the conventional turbo MMSE (minimum mean square error) equalizer and is also with better bit error rate (BER) performance than that of the conventional adaptive turbo MMSE equalizer. Simulation results confirm the effectiveness of the proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1659-1666
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• 1998

The multicode CDMA systems that are widely studied as an effective transmission methodology in the IMT-2000 systems, employ orthogonal codes to transform high rate data into parallel, low rate data for simultaneous transmission. In this paper, we propose a new multicode CDMA system which achieves the same data rate and processing gain of the conventional systems, while significantly improves bit error rate performance by exploiting a convolutional code with code rate r=1/2 and a bi-orthogonal code. The simulation results for synchronous systems using maximal ratio combining Rake receivers under additive white Gaussian noise and multi-path fading channels, show significant improviements by the proposed system.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.75-77
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• 2012

In recent years, with the development of various transportation, railway evolved a lot. With advanced rail system, efficient communication system was required. for the delivery of accurate information of railway communications systems. Accordingly, railway communication system has evolved in a variety of ways. Cooperative communication method was proposed railway minimize the effects of fading in wireless communications and more efficient communication. In this paper, we present cooperative transmission techniques and channel characteristics and examples, and simulation results.

• Proceedings of the IEEK Conference
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• 2003.11a
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• pp.263-266
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• 2003

In this paper, we propose a new progressive image transmission system including the image coding scheme that efficiently uses the relationship between the properties of a spatial image and its wavelet transform. Firstly, an original image is decomposed into several layers by the wavelet transform, and simultaneously decomposed into 2"x2" blocks. Each image is classified into two image types according to the standard deviations of its blocks. And then each block is categorized into two regions by different thresholds according to the image types, i.e., significant activity region (SAR) and insignificant activity region (IAR). Simulation results show that the proposed coding method has better performance than the EZW and SPIHT in terms of image quality and transmitted bit-rate. In addition, it can be applied to the applications requiring the progressive image transmission.nsmission.