• Journal of the Korea Institute of Information Security & Cryptology
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• v.6 no.4
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• pp.3-38
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• 1996

The mobile station shall convolutionally encode the data transmitted on the reverse traffic channel and the access channel prior to interleaving. Code symbols output from the convolutional encoder are repeated before being interleaved except the 9600 bps data rate. All the symbols are then interleaved, 64-ary orthogonal modulation, direct-sequence spreading, quadrature spreading, baseband filtering and QPSK transmission. The sync, paging, and forward traffic channel except the pilot channel in the forward CDMA channel are convolutionally encoded, block interleaved, spread with Walsh function at a fixed chip rate of 1.2288 Mcps to provide orthogonal channelization among all code channels. Following the spreading operation, the I and Q impulses are applied to respective baseband filters. After that, these impulses shall be transmitted by QPSK. Authentication in the CDMA system is the process for confirming the identity of the mobile station by exchanging information between a mobile station and the base station. The authentication scheme is to generate a 18-bit hash code from the 152-bit message length appended with 24-bit or 40-bit padding. Several techniques are proposed for the authentication data computation in this paper. To protect sensitive subscriber information, it shall be required enciphering ceratin fields of selected traffic channel signaling messages. The message encryption can be accomplished in two ways, i.e., external encryption and internal encryption.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1325-1341
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• 1998

A conventional CBR channel is now capable of delivering several digitally compressed video programs due to recent advances in video compression, such as MPEG-2, and digital transmission technology. This paper presents a joint video coding scheme that is to maintain a constant sum of bit rates for all the programs but to allow the variable bit rate for individual program in the transimission environment mentioned above. Thus advantages of VBR video compression can be obtained. This paper contributes in two aspects. First, a rate-distortion estimation method for MPEG-2 video is proposed, which enavle us predict the amount of bits and the distortion generated from an encoded picture at a given quantization step size and vice versa. The most attractive features of the proposed rate-distortion estimation method are its accuracy and a computational complexity low enough to be applied to real-time video coding applications. Second, this paper presents an efficient and accurate joint rate control scheme using the rate-distortion estimation results and verifies its performance with experiments. The experimental results show that our coding scheme gives a significant gain even though a small number of video programs are coded jointly. For example, a stable picture quality is maintained among the video programs as well as within a program, and additional extra programs can be transmitted over the same channel bandwidth if the proposed joint video coding scheme is used.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.11
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• pp.84-91
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• 2009

A high speed serial link transmitter using multi-level signaling is proposed. To achieve high data rate m high speed serial link, 4-pulse amplitude modulation (PAM) is used. By transmitting 2 bit data in each symbol time, high speed data transmission, two times than binary signaling, is achieved. The transmitter transmits current-mode output instead of voltage-mode output Current-mode output is much faster than voltage-mode output, so higher data transmission is available by increasing switching speed of driver. $2^5-1$ pseudo-random bit sequence (PRBS) generator is contained to perform built-in self test (BIST). The 4-PAM transmitter is designed in Dongbu HiTek $0.18{\mu}m$ CMOS technology and achieves 8 Gb/s, 160 mV of eye height with 1.8 V supply voltage. The transmitter consumes only 98 mW for 8 Gb/s transmission.

• Speech Sciences
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• v.11 no.4
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• pp.67-73
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• 2004

Packet loss, jitter, and delay in the Internet are caused mainly by the shortage of network bandwidth. It is due to queuing and routing process in the intermediate nodes of the packet network. In the Internet whose bandwidth is changing very rapidly in time depending on the number of users and data traffic, controlling the peak transmission bit-rate of a VoIP. system depending on the channel condition could be very helpful for making use of the available network bandwidth. Adapting packet size to the channel condition can reduce packet loss to improve the speech quality. It has been shown in [1] that a VoIP system with an AMR speech codec provides better speech quality than VoIP systems with fixed rate speech codecs. With the adaptive codec mode assignment. algorithm proposed in [1], in this paper, we performed the voice transmission experiments using the wireless LAN through the real Internet environment. Experimental results are analyzed and discussed with our findings.

• Journal of Digital Contents Society
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• v.12 no.4
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• pp.485-490
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• 2011

Smoothing is a transmission plan where variable rate video data is converted to a constant bit rate stream. These smoothing algorithms include CBA, MCBA, MVBA, PCRTT and others. But, these algorithms build a transmission plan per frame unit. So, these algorithms cause frame burst or GOP burst. In order to improve it, MVBAG algorithm build a transmission plan per GOP. But this algorithm may not guarantee QoS when frame's size is abruptly larger or smaller than the computed transmission rate. In this paper, a smoothing algorithm is proposed to enhance MVBAG algorithm's problem. In order to show the proposed algorithm's performance, the proposed algorithm is compared with MVBAG algorithm using various evaluation factors such as number of frames that do not meet the QoS, average transmission rate variability per frame, average transmission rate variability per GOP. Experimental results show that the proposed algorithm outperforms MVBAG algorithm in number of frames that do not meet the QoS.

• The Journal of the Acoustical Society of Korea
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• v.15 no.6
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• pp.59-65
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• 1996

This paper proposes a 4 kbps PSI-VSELP(Pitch Synchronous Innovation-Vector Sum Excited Linear Prediction) speech coder which produces speech equivalent to that of the conventional 4.8 kbps VSELP. Since the 'half-rate' is differently defined from country to country, there may be a need to reduce the bit rate of conventional half-rate coder. To minimize the degradation of speech quality caused by bit-rate reduction, it is desirable to perform bit-allocation based on the carefull consideration of the effect of various transmission parameters. This paper adopts this analytical approach for bit-allocation at 4 kbps. To improve the quality of the VSELP coder at 4 kbps, basis vectors which play the most important role in the performance, are optimized by an iterative closed-loop training process and the PSI technique is employed in the VSELP performance, are optimized by an iterative closed-loop training process and the PSI technique is employed in the VSELP coder. To demonstrate the performance of the proposed speech coder, we peformed experiments under the noiseless and error free conditions. From experimental results, even though the proposed 4 kbps PSI-VSELP coder showed lower scores in the objective measure, higher scores in subjective measure was obtained compared with those of the conventional 4.8 kbps VSELp.

• Journal of IKEEE
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• v.2 no.2 s.3
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• pp.194-199
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• 1998

In the atmospheric wireless optical communication system, the low power transmission can be accomplished by the high directivity of laser beam. But, the transmitted optical signal undergoes the serious influences by the atmospheric effects like absorption, scattering, and turbulence because the transmission channel is the atmospheric space. In this paper, therefore, we obtain the link equation for an atmospheric wireless optical LOS communication link under the atmospheric effects and find the repeaterless transmission length to estimate the system performance through the computer simulation. From the results of the computer simulation, we present the transmission length that is possible to transmit without a repeater at given data rates and know that data rate is decreased rapidly when the transmission length is increased slightly at given bit error rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2563-2578
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• 1996

In this paper, channel error characteristics are investigated to alleviate the channel error propagation problem of the digital TV transmission systems. First, error propagation problems, which are mainly caused by the inter-frame dependancy and variable length coding of the MPEG-2 baseline encoder, are intensively analyzed. Next, existing channel resilient schemes are systematically classified into two kinds of schemes; one for the encoder and the other for the decoder. By comparing the performance and implementation cost, the encoder side schemes, such as error localization, layered coding, error resilience bit stream generation techniques, are described in this paper. Also, in an effort to consider the parcticality of the real transmission situation, an efficient error detection scheme for a decoder system is proposed by employing a priori information of the bit stream syntas, checking the encoding conditions at the encoder stage, and exploiting the statistics of the image itself. Finally, subsequent error concealment technique based on the DCT coefficient recovery algorithm is adopted to evaluate the performance of the proposed error resilience technique. The computer simulation results show that the quality of the received image is significantly improved when the bit error rate is as high as 10$^{-5}$ .

• Journal of Astronomy and Space Sciences
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• v.27 no.3
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• pp.221-230
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• 2010

A 4+12+16 amplitude phase shift keying (APSK) modulation outperforms other 32-APSK modulations in a nonlinear additive white Gaussian noise (AWGN) channel because of its intrinsic robustness against AM/AM and AM/PM distortions caused by the nonlinear characteristics of a high-power amplifier. Thus, this modulation scheme has been adopted in the digital video broadcasting-satellite2 European standard. And it has been considered for high rate transmission of telemetry data on deep space communications in consultative committee for space data systems which provides a forum for discussion of common problems in the development and operation of space data systems. In this paper, we present an improved bits-to-symbol mapping scheme with a better bit error rate for a 4+12+16 APSK signal in a nonlinear AWGN channel and propose a simple signal detection algorithm for the 4+12+16 APSK from the presented bit mapping.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.277-282
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• 2005

The arrangement of I-picture starting times of multiplexed variable bit .ate (VBR) MPEG videos may significantly affect the cell loss ratio (CLR) characteristics of the multiplexed traffic. This paper presents an efficient I-picture arrangement method which can minimize the CLR of the multiplexed traffic when multiple VBR MPEG videos are multiplexed onto a single constant bit rate link. In the proposed method, we use the probability that the arrival rate exceeds the link capacity as the measure for the CLR of the multiplexed traffic. Simulation results show that the proposed method can find more optimal arrangement than existing methods in respect of the CLR.