• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.1123-1131
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• 2005

In this paper, optimal position of optical phase conjugator (OPC) for best compensating distorted WDM channels due to both chromatic dispersion and self phase modulation (SPM) in $8{\times}40$ Gbps WDM systems is numerically investigated, and the eye opening penalty (EOP) and bit error rate (BER) characteristics of overall WDM channels at this position is investigated, comparing with that in case of OPC placed at mid-way of total transmission length. It is confirmed that the compensation extents in WDM system with OPC is more improved by the shifting OPC position from the mid-way of total transmission length, depending on the modulation format and fiber dispersion coefficient. Ant it is confirmed that, from a viewpoint of the reception performance, EOP of each channel is more or less different with one another, but the BER characteristics of overall channels are almost equal.

• ETRI Journal
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• v.41 no.2
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• pp.184-196
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• 2019

Wavelet packet modulation (WPM) is a multicarrier modulation (MCM) technique that has emerged as a potential alternative to the widely used orthogonal frequency-division multiplexing (OFDM) method. Because WPM has overlapped symbols, equalization cannot rely on the use of the cyclic prefix (CP), which is used in OFDM. This study applies linear minimum mean-square error (MMSE) equalization in the time domain instead of in the frequency domain to achieve low computational complexity. With a modest equalizer filter length, the imperfection of MMSE equalization results in subcarrier attenuation and noise amplification, which are considered in the development of a bit-loading algorithm. Analytical expressions for the bit error rate (BER) performance are derived and validated using simulation results. A performance evaluation is carried out in different test scenarios as per Recommendation ITU-R M.1225. Numerical results show that WPM with equalization-aware bit loading outperforms OFDM with bit loading. Because previous comparisons between WPM and OFDM did not include bit loading, the results obtained provide additional evidence of the benefits of WPM over OFDM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.8C
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• pp.810-823
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• 2005

The transmission of duplicate packets provides a great loss-resilience without undue time-delay in the video transmission over packet loss networks. But this method generally deteriorates the problem of traffic congestion because of the increased bit-rate required for duplicate transmission. In this paper, we propose an efficient packetization and duplicate transmission of video packets. The proposed method transmits only the video signal with high priority for each video macroblock that is quite small in volume but very important for the reconstruction of the video. The proposed method significantly reduces the required bit-rate for duplicate transmission. An efficient packetization method is also proposed to reduce additional packet overhead which is required for transmitting the duplicate data. The duplicated high priority data of the Previous video slice is transmitted as a Piggyback to the data Packet of the current video slice. It is shown by simulations that the proposed method remarkably improves the packet loss-resilience for video transmission only with small increase of redundant duplicated data for each slice.

• Journal of the Korean Society of Radiology
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• v.5 no.6
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• pp.329-334
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• 2011

This paper presents improvement of compression rate for SPIHT algorithm based on wavelet compression through redundancy bit removing. Proposed SPIHT algorithm uses a method to select of optimized threshold from feature of wavelet transform coefficients and removes sign bit only if coefficient is LL area. Finally Proposed SPIHT algorithm applies to Huffman coding. Experimental results show that the proposed algorithm achieves more improvement bit rate and more fast progressive transmission with low bit rate.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.156-163
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• 2005

In this paper, we analyzed the performance of VDL mode 3 system model whose specification is defined by ICAO(International Civil Aviation Organization). For performance evaluation, we obtained BER(Bit Error Rate), transmission delay time, burst retransmission rate and throughput. From the analysis result, we could explicitly define relationships among BER, transmission delay time, throughput and burst restransmission rate. In addition, it became known that V/D retransmission rate and throughput are closely related in down link channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1059-1066
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• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.668-672
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• 2009

In wireless ad-hoc network, knowing the available bandwidth of the time varying channel is imperative for live video streaming applications. This is because the available bandwidth is varying all the time and strictly limited against the large data size of video streaming. Additionally, adapting the encoding rate to the suitable bit-rate for the network, where an overlarge encoding rate induces congestion loss and playback delay, decreases the loss and delay. While some effective rate controlling methods have been proposed and simulated well like VTP (Video Transport Protocol) [1], implementing to cooperate with the encoder and tuning the parameters are still challenging works. In this paper, we show our result of the implementation experiment of VTP based encoding rate controlling method and then introduce some techniques of our parameter tuning for a video streaming application over wireless environment.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.10
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• pp.1225-1233
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• 1988

In this paper, several simple approaches to Laplacian pyramid coding have been presented for obtaining reasonably acceptable image quality even at low bit rates of 0.3-0.5 bits/pel. For this purpose, the feedback construction of each Lapliacian plane, 3-dimensional prediction and three-level center-clipping quantization are introduced into the coding procedures. For greatly reducing the bit rate of the bottom layer, two new schemes of conditional transmission and edge sharpening without transmission are used. In experiments, our latter sheme has yielded the total bit rate of about 0.3 bits/pel while retaining reasonably acceptable image quality.

• Journal of Korean Institute of Industrial Engineers
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• v.14 no.1
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• pp.1-15
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• 1988

DS1 transmission systems use framing bit errors, bipolar violations and code-detected errors to estimate the bit error rate when determining errored and severely errored seconds. Using the coefficient of variation under the memoryless binary symmetric channel assumption, a basic framework to evaluate these estimation schemes is proposed to provide a practical guideline in determining errored and severely errored seconds which are fundamental in monitoring the real-ime error performance of DS1 transmission systems carrying live traffic. To evaluate the performance of the cyclic redundancy check code (CRC), a computer simulation model is used. Several drawbacks of the superframe format in association with real time error performance monitoring are discussed. A few recommendations are suggested in measuring errored and severely errored seconds, and determining service limit alarms through the use of the superframe format. Furthermore, we propose a new robust scheme for determining service limit alarms which take into consideration the limitations of some estimation schemes for the time interval of one second.

• ETRI Journal
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• v.28 no.1
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• pp.17-30
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• 2006

In time division duplex (TDD) code division multiple access (CDMA) systems, chip-synchronous transmission in the uplink is obtainable, thus leading to free multiple access interference in flat Rayleigh fading channels plus additive white Gaussian noise. This motivates us to develop a novel cooperative transmission strategy that allows single-antenna devices to benefit from spatial diversity using orthogonal signature sequences. The proposed cooperation is applicable to many digital modulation methods and achieves the fullest diversity level, low implementation complexity, and a full data rate. Closed-form bit-error-rate expressions were also derived and compared to simulation results in order to evaluate its validity. A variety of numerical results demonstrated the cooperation's superiority over single transmission under the same transmit power constraint.