• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.5
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• pp.917-922
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• 2018

In the conventional interchannel interference self-cancellation (ICI-SC) schemes, the length of sampling window is the same as the symbol length of orthogonal frequency division multiplexing (OFDM). Thus, the number of complex operations to compute the interference coefficient of each subchannel is significantly increased. To solve this problem, we present an approximated mathematical model for the coefficients of ICI-SC schemes. Based on the proposed approximation, we analyze mean squared error (MSE) and computational complexity of the ICI-SC schemes with the length of sampling window. As a result, the presented approximation has an error of less than 0.01% on the MSE compared to the original equation. When the number of subchannels is 1024, the number of complex computations for the interference coefficients is reduced by 98% or more. Since the computational complexity can be remarkably reduced without sacrificing the self-cancellation capability, it is considered that the proposed approximation is very useful to develop an algorithm for the ICI-SC scheme.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.1105-1108
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• 1998

본 논문은 VSB 전송방식의 HDTV 수신기에 입력되는 신호의 위상잡음 및 이득오차를 없애주는 위상 추적 루프를 설계하였다. 위상 추적 루프는 VSB 신호가 가지는 신호점과 입력된 I 채널의 표본화된 데이터를 이용하여 신호점들의 Q 채널 성분을 추정한 다음 복소곱셈기를 이용하여 입력신호와 곱합으로써 위상의 에러값을 보상하는 구조로 되어 잇다. 위상오차를 검출하는 알고리즘으로 시그늄 함수를 이용함으로써 하드웨어의 부담을 줄이면서 넓은 선형영역을 가질 수 있게 되어 우수한 추적 성능을 가지는 위상 추적 루프를 구현하였고 소프트웨어 심류레이션을 통하여 제시한 알고리즘의 효율성을 입증한 후 ASIC으로 구현하였다.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.372-375
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• 2001

본 논문에서는 고속데이터 전송을 위한 CDMA 모뎀를 구현하였다. 데이터율 1Mbps의 트래픽 5채널에 직교부호를 곱하여 채널을 구분한 후 하나의 채널로 처리하였다. I,Q로 입력된 신호는 복소 곱셈기에서 칩 레이트 8Mcps로 OCQPSK(또는 HPSK) 변조하였다. 복조기는 I,Q의 신호를 역확산한 후 직교부호를 다시 곱하여 각 채널의 데이터를 분리한다. 변복조기의 구현은 클럭 속도 167MHz의 부동 소수점형 프로세서인 TI사의 TMS320C6701 DSP(Digital Signal Processor)를 사용하었고, long code 및 I,Q 채널 PN 코드는 IMT-2000 동기방식과 비동기방식의 규격에 정의된 2가지의 PN코드 발생기를 모두 구현하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.6
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• pp.1231-1243
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• 1997

Digital satellite communication channels have nonlinearities with memory due to saturation characteristics of traveling wave tube amplifier in the satellite and transmitter/receiver linear filters. In this paper, we propose a network structure and a learning algorithm for complex pi-sigma network (CPSK) and exploit CPSN in the problem of equalization of nonlinear satellite channels. The proposed CPSN is a complex-valued extension of real-valued pi-sigma network that is a higher-order feedforward network with fast learning while greatly reducing network complexity by utilizing efficient form of polynomials for many input variables. The performance of the proposed CPSN is demonstrated by computer simulations on the equalization of complex-valued QPSK input symbols distorted by a nonlinear channel modeled as a Volterra series and additive noise. The results indicate that the CPSN shows good equalization performance, fast convergence, and less computations as compared to conventional higher-order models such as Volterra filters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.235-239
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• 2008

In this paper, we study a simulation model for cooperative MIMO (multiple-input multiple-output) channels and present a cooperative one-ring channel model which is extended from the geometrical one-ring and two-ring scattering models. Assuming that the source, the destination and the relay are surrounded by an infinite number of scatters, we derive a reference model for the cooperative one-ring channel and propose a simulation model based on the reference model provided in the paper. Then we show how modeling parameters of the simulation model are determined to match the correlation functions for the respective models. With numerical investigation, we also show that the correlation functions for the reference and the simulation are well matched.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.9
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• pp.11-20
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• 1998

High-speed complex-number arithmetic units are essential to baseband signal processing of modern digital communication systems such as channel equalization, timing recovery, modulation and demodulation. In this paper, a new complex-number multiplication algorithm is proposed, which is based on redundant binary (RB) arithmetic combined with radix-4 Booth recoding scheme. The proposed algorithm reduces the number of partial product by one-half as compared with the conventional direct method using real-number multipliers and adders. It also leads to a highly parallel architecture and simplified circuit, resulting in high-speed operation and low power dissipation. To demonstrate the proposed algorithm, a prototype complex-number multiplier-accumulator (CMAC) core with 10-bit operands has been designed using 0.8-$\mu\textrm{m}$ N-Well CMOS technology. The designed CMAC core contains about 18,000 transistors on the area of about 1.60 ${\times}$ 1.93 $\textrm{mm}^2$. The functional and speed test results show that it can operate with 120-MHz clock at V$\sub$DD/=3.3-V, and its power consumption is given to about 63-mW.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.503-512
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• 2001

A new adaptation algorithm for the digital predistorter is presented. The proposed technique employs the real-time transmitted signals through HPA for the table update. Hence the proposed algorithm does not depend on modulation format and the signal transmission of HPA is not affected during the adaptation process. The experimental results are presented to verify the proposed method and we obtained about 8.4 dB of ACPR improvement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.72-78
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• 2006

It is impossible to provide full diversity and full rate simultaneously using more than two transmit antennas in transmit diversity system. To do this, simple interference cancellation scheme and transmit power allocation scheme have been proposed, recently. But the former has increased noise power and the latter has increased interference which is induced by other channel in fading channel. In this paper, we propose an adaptive transmit power allocation algorithm to minimize the estimation error in the channel environments which have different fading levels each other and to improve the system performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.2
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• pp.151-160
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• 1997

In this paper, we have carried out the DS/CDMA with a suppressed pilot channel, which is used in receiving coherently with Rake diversity and in synchronizing the chip timing, in the mobile satellite communication. Also, we have investigated the envelope variation of a shadowed Rician fading simulator, and analyzed the error performences of DS/CDMA in the mobile satellite communication. The results showed that the error performance in the Heavy shadowing environment might be degraded more than in the Rayleigh fading environment since the fading envelopes in the former environment are varied randomly compared with those in the latter environment. And the performence of DS/CDMA system could be improved about 10 dB compared with that of narrowband QPSK system. In conclusion, DS/CDMA with a suppressed pilot channel had the best performance in the case of the suppressed pilot channel to transmission power ratio $\beta$=-8 dB, the number of complex delay profiles $N_{profile}$=32, and using these values, the error performance of DS/CDMA in Light shadowing environment was identical to the ideal QPSK error performance.

• The Journal of the Acoustical Society of Korea
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• v.23 no.1
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• pp.17-23
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• 2004

The mobile radio channel can be simulated as a complex-valued random process with narrow-band spectrum. This paper describes a real-time implementation of that process using a INS320C6414 digital signal processor and XC2VP30 Virtex FPGA. The simulator presented here is not only a comprehensive model of the flat fading but also frequency selective fading mobile channel conditions. To replicate the statistical characteristics of the multipath fading environment with the minimum computational burden, multi-rate techniques are employed to resolve practical problems such as variable sampling rate. The simulator produces accurate and consistent results due to digital implementation. It is very flexible and simple to program for various field conditions in mobile communications with a graphical user interface.