• Journal of Broadcast Engineering
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• v.10 no.3
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• pp.261-269
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• 2005

Throughout the history of digital communication, the digital speech coder is used as speech compression tool. Nowadays, the speech coder has been rapidly developed in the area of mobile communication system to overcome severe channel error and limitation of radio frequency resources. Due to the development of high performance communication system, high quality of speech coder is needed. This kind of speech coder can be used not only in communication services but also in digital multimedia services. In this paper, we describe the technologies of digital speech coder which are used in wire and wireless communication. We also present a summary of recent speech coding standards for narrowband and wideband applications. Finally we introduce the technical trends of next generation speech coder.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.219-226
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• 2021

LED-to-LED VLC is a technology that uses LEDs as both a transmitter and a receiver unlike the typical VLCs. In this paper, we experimentally demonstrate a micro LED-to-LED VLC using Micro LED. We tested all the possible VLC cases using red, yellow, green, blue, and white color LED as both a transmitter and a receiver, and measured rise time and SNR. Then we calculated channel capacity depending on the LED color sets. Our experimental results show that the best channel capacity is 125 kbps when the transmitter micro LED was blue and the receiver LED was green. We also measured BERs of VLCs using OFDM signal, and we showed a successful micro LED-to-LED VLC upto 250 kbps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.12
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• pp.1806-1814
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• 1993

Efficient speech coders using tree coding combined with harmonic scaling are designed at the rate of 4.8 kilobitts/sec (kbps). A time domain harmonic scaling algorithm (TDHS) is used to compress input speech by a factor of two. This process allows the tree coder have 1.5 bits/sample for 4.8 kbps in the case of a 6.4 kHz sampling rate. In the backward adaptive tree coder, there are three components of the code generator, including a hybrid adaptive quantizer, a short-term predictor and a pitch predictor. The robustness of the tree coder is achieved by carefully choosing the input of the short term predictor adaptation. Also, inclusion of a smoother in the pitch predictor improves the error performance of tree coder in the noisy channel. Subjectively, tree coding combined with TDHS provides good quality speech at 4.8 kbps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4B
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• pp.345-352
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• 2002

In this paper, in order to evaluate the performance of IS-95 system reverse link in white gaussian noise and rayleigh fading environment, we suggest epochal proposal to improve computer run-time and its efficiency is verified in terms of the number of samples. MC(Monte Carlo) simulation is the most popular simulation technique lately, but MC simulation requires a number of samples at low bit error rate. Therefore, MC cannot avoid the limit of computer run-time. To alleviate these problems, we apply the suggested method called central moment technique to the reverse link of the IS-95 system and can obtain discrete probability mass functions from Nth order central moments of the less number of received signal samples than those required in MC. Continuous cumulative probability distribution function can be accurately estimated by using interpolation and the improvement effect for the number of samples is proven.

• Journal of Advanced Navigation Technology
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• v.16 no.6
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• pp.982-987
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• 2012

In this paper, the SNR estimation error of Decision Directed SNR estimation method in AWGN is investigated, which uses samples received in reference decision region. In communication system receiver, when SNR estimation scheme using error vectors between ideal sample points and received sample points of reference region is adopted, the samples contain incorrectly received samples due to AWGN. Consequently, the mean of estimated reference constellation point is shifted and Decision Directed SNR estimation is inaccurately performed. These effects are explained by modified probability density function and difference between actual SNR and estimated SNR is theoretically derived and quantatively analyzed. It is proved that SNR estimation error obtained through computer simulation is matched up with derived one, and SNR estimation performance is enhanced significantly by adopting suggested correction scheme.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.159-167
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• 2006

In this paper the numerical methods of finding the optimal position of optical phase conjugator (OPC) and the optimal fiber dispersion are proposed, which are able to effectively compensate overall channels in $16{\times}40$ Gbps WDM system. And the compensation characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to confirm the availability of the proposed methods. It is confirmed that the reception performances are largely improved in the system with the induced optimal parameters than in the system with MSSI through the analyzing the eye opening penalty (EOP) and bit error rate (BER) characteristics. It is also confirmed that two optimal parameters depend on each other, but are less related with the procedural problem about the first optimal value among these.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.148-156
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• 2003

This paper describes the RF performance issues of UE for W-CDMA system based on 3 GPP specifications. The parameters of transmitter and receiver are derived from the viewpoint of RF performance. In order for UE to achieve high performance, the transceiver performance requirements such as ACLR, EVM, Peak Code Domain Error, spectrum emission mask, frequency error stability and TX power control dynamic range for transmitter and reference sensitivity level, blocking characteristics, noise figure, ACS, AGC dynamic range for receiver are considered. On the basis of the required parameters, the UE RF transceiver is implemented and then the evaluation of RF performance is accomplished through practical test scenarios.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.110-118
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• 2013

This paper describes the development of DSSS wireless communication uplink system for missile remote control. In consideration of low probability of intercept, low probability of exploitation, anti-jam, low latency, and doppler frequency offset, we used DSSS partially DBPSK. Also we used the selective diversity with two receiving antennas to mitigate multipath interference which is the dominant channel impairment and the turbo product code(TPC) for forward error correction(FEC) to improve bit error rate performance.

• Proceedings of the Korea Contents Association Conference
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• 2006.05a
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• pp.132-135
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• 2006

Recently, multimedia data service using mobile terminal has been increased according to the development of wireless network technology which can be used in an indoor or outdoor environment. However, the wireless network shares the channel and it has a high error rate because of characteristics of transmission media. Therefore, it has a lot of problems for guaranteeing QoS(Quality of Services) in various requirements. This paper suggests a CSD-WRR(Channel State Dependent-WRR) method for compensating the service rate considering the transmission deadline. Simulation results show that the suggested method outperforms the conventional WRR in the view of the deadline miss rate and fairness.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.11
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• pp.2465-2473
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• 2012

Recently, as one of low complexity video encoding methods, DVC (Distributed Video Coding) scheme has been actively studied. Most of DVC schemes exploit feedback channel to achieve better coding performances, however, this causes these schemes to have high decoding delay. In order to overcome these, this paper proposes a new fast DVC decoding method using parity-bit request model, which can be obtained by using bit-error rate, sent by encoder with motion vector, which is transmitted through feedback channel by decoder after generating side information. Through several simulations, it is shown that the proposed method improves greatly the decoding speed, compared to the conventional schemes.