• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10C
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• pp.1010-1018
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• 2007

In this paper, we propose a companding scheme to effectively reduce PAPR (Peak-to-Average Power Ratio) of the OFDM (Orthogonal frequency Division Multiplexing) signals. The proposed scheme is basically based on the companding scheme to consider both complexity and Bit Error Rate (BER) performance, and composed of the clipping followed by the companding scheme. In the first step of the proposed scheme, some of peak signals which do not influence the BER even without them, are clipped. In the second step, the proposed scheme utilizes the ${\mu}-law$ companding to effectively reduce the PAPR. Simulation results show that the proposed clipped companding scheme can provide more PAPR reduction without degradation of the BER performance, as compare to the conventional ${\mu}-law$ companding.

• ETRI Journal
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• v.46 no.4
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• pp.595-603
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• 2024

This paper presents methods for reducing the peak-to-average power ratio (PAPR) of the orthogonal time frequency space (OTFS) signal. These methods mainly consist of two operations: symbol interferometry (SI) and either 𝜇-law or A-law companding. SI spreads the data of one OTFS symbol onto all symbols and is implemented using a simple inverse fast Fourier transform operation on each OTFS symbol. During the second operation, the PAPR of the OTFS signal is significantly reduced. For our performance analysis, the complementary cumulative distribution function, probability density function, and bit error rate are illustrated through simulations performed in MATLAB. The performance is also analyzed using a solid-state power amplifier at the transmitter and compared with OTFS, 𝜇-law-based OTFS, and SI OTFS systems. The results indicate that the proposed OTFS system achieves a low PAPR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.2
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• pp.202-206
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• 1993

To secure the 64 kbps clear channel capability in the ISDN, it was decided to convert its North American digital transmission system into the European system especially in DS1 level. But their different companding law became an issue in the process of R&D in the existing time division digital switch such as TDX-1 to incorporate it into the ISDN. TDX-1 has been installed with North American ${\mu}$ companding law and its ISDN capability is under development now. Thus, because of the ${\mu}$ law/A law conversion for the interworking of two different transmission system, it is difficult to maintain the ISDN B channel transparency between TDX-1 and new European system with A companding law. Among some solutions for it, European frame format with ${\mu}$ law companding is recommended. Those problems and solutions are presented in this paper.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.7 no.2
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• pp.47-54
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• 1982

In this paper, a improved per-channel PCM Coder with 1-bit interpolation is proposed. The coder converts a telephone signal to 15-segments u-law PCM signal of a large dynamic range. The A/D conversion technique of the proposed converter requires a feedback loop around a quantizer operates at high speed, and a accumulater for accumulating the quantized values to provide PCM outputs. To obtain both linear and compressed PCM signals a improved table look-up method is presented. The operations of the proposed converter are certified through the experiments to be good. The experimental circuit comprises TTL logic gates, a resistive D/Z converter and a simple differential amplifier. From the results of the experiments, it is known that the proposed converter has many advantage to be adopted economically for per-channel onverter used in rural area service.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1750-1754
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• 2013

A variable bit rate speech coder is presented. The coder is based on the observation that a speech signal can be viewed as a combination of piecewise linear signals in a short time period. The encoder detects the sample points where the slope of the signal changes, which are called the inflection points in this paper. The coder transmits the location and value for the detected inflection sample, but only the location information for the noninflection samples. In the decoder, the noninflection samples are estimated with interpolation of the received information. Several factors affecting the performance of the coder have been tested through simulation. Simulation results show that the linear interpolation produces 1 ~ 5 dB improvement over the cubic spline interpolation. And the -law companding does not provide any benefit when it is applied before the inflection detection. With low threshold values in the inflection point detection, the coder shows better MOS and more than 16 dB improvement in SNR compared to the continuously variable slope delta modulation (CVSDM).