• ETRI Journal
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• v.30 no.6
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• pp.850-852
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• 2008

This letter presents a power efficient 64-state Viterbi decoder (VD) employing a two-stage radix-4 add-compare-select architecture. A class of VD architectures is implemented, and their hardware complexity, maximum operating speed, and power consumption are compared. Implementation results show that the proposed VD architecture is suitable for multiband orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) systems, which can support the data rate of 480 Mbps even when implemented using 0.18-${\mu}m$ CMOS technology.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2286-2292
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• 2008

In this paper, we design a RS(23,17) decoder for MB-OFDM(Multiband-Orthogonal Frequency Division Multiplexing) system, in which Modified Euclidean(ME) algorithm is adopted for key equation solver block. The proposed decoder has been optimized for MB-OFDM system so that it has less latency and hardware complexity. Additionally, we have implemented the proposed decoder using Verilog HDL and synthesized with Samsung 65nm library. From synthesis results, it can operate at clock frequency of 250MHz, and gate count is 20,710.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.648-653
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• 2011

We propose a new frequency offset estimation technique for multiband orthogonal frequency modulation (MB-OFDM) based ultra wideband (UWB) systems. The proposed frequency offset estimation technique is related to the scheme of Schmidl for channel model 1 (4-1Om NLOS, rms. delay =14.3ns.) using more than two symbols and with alternate symbols. Variance of frequency offset estimate obtained from the proposed frequency offset estimation technique approaches very nearing to Cramer Rao Lower Bound (CRLB) in an AWGN channel. BER performance of the proposed technique is also presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.613-616
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• 2008

In this paper, a fine residual frequency offset estimation scheme is proposed for multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the MB-OFDM UWB system, thus removing the need of pilot symbols. The mean square error of the synchronization scheme is evaluated and simulation results are used to verify the effectiveness of the proposed estimator. When compared to the pilot-aided conventional estimator, the proposed estimator has a lower estimation error.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2119.1_2120.1
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• 2009

UWB(Ultra Wide Band)는 차세대 무선통신 기술로 무선 디지털펄스라고도 한다. GHz대의 주파수를 사용하면서도 초당 수천~수백만 회의 저출력 펄스로 이루어진 것이 큰 특징이다[1]. 기존 무선통신 기술의 양대 축인 IEEE 802.11과 블루투스 등에 비해 속도와 전력소모 등에서 월등히 앞서고 있으며, SoC(System on a Chip)의 저전력 구현에 대한 연구가 활발히 진행되고 있다. OFDM은 크게 FFT(Fast Fourier Transform) 블록, Interpolation /decimation 필터 블록, 비터비 블록, 변복조 블록, 등화기 블록 등으로 구성된다. 고속 시스템에서는 대역효율성이 우수한 OFDM(Orthogonal Frequency Division Multiplexing) 방식을 사용하고 있으며, OFDM 전송방식은 직렬로 입력되는 데이터 열을 병렬 데이터 열로 변환한 후에 부반송파에 실어 전송하는 방식이다. 이와 같은 병렬화와 부반송파를 곱하는 동작은 IFFT와 FFT로 구현이 가능한데, FFT 블록의 구현 비용과 전력소모를 줄이는 것이 핵심사항이라고 할 수 있다. 기존논문에서는 OFDM용 FFT 구조로 단일버터플라이연산자 구조, 파이프라인 구조, 병렬구조 등의 여러 구조가 제안되었다[2]. 본 논문에서는 Radix-8 FFT 알고리즘 기반의 New partial Arithmetic 저전력 FFT 구조를 제안하였다. 제안한 New partial Arithmetic 저전력 FFT구조는 곱셈기 대신 병렬 가산기를 이용 하여 지금까지 사용되는 FFT 구조보다 전력소모를 줄일 수 있음을 보였다.

• 전자공학회논문지 IE
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• v.47 no.3
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• pp.35-40
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• 2010

In this paper, we propose an algorithm to improve the precision of initial carrier-frequency offset estimation for multiband-OFDM (MB-OFDM) UWB system which is considering the quantization-noise effect. In the general OFDM system, the two adjacent and repeated preamble symbols are used for the initial carrier-frequency synchronization while the performance of the frequency-offset estimation is bounded by quantization effect generated from analog-to-digital conversion at the receiver. This paper proposes a method in which one-symbol interval between two adjacent preamble symbols for the initial frequency synchronization is extended to multiple-symbol interval between non-adjacent symbols in an extent that phase ambiguity does not occur. In this paper, we also present '6' as optimal multiple symbol interval for the MB-OFDM system with 30 preamble symbols on 3-band hopping and with 4-bit A/D conversion at the receiver. Under the channel environments for the MB-OFDM UWB system, the simulation results show that the proposed estimation algorithm can achieve the initial estimation in offset precision less than 5 ppm.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.6 no.3
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• pp.111-121
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• 2007

In this paper, we propose a TH-Multiband-UWB system through pulse shaping to fit in domestic UWB spectrum regulation. We propose the transmission pulse of Multi-Carrier type for pulse shaping and use Cognitive Radio to detect interfering frequency. We use Genetic Algorithm in Cognitive Radio's calculation propose and propose solution of interference problem between TH-UWB using Cognitive Radio and typical MB-OFDM UWB system or other communication systems. In this paper, we explain how Cognitive Engine detects the interfering frequency. The technique of TH-Multiband-UWB system using Cognitive Radio shows a good performance in interference condition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1275-1284
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• 2010

100 MHz bandwidth and 1 Gbit/s data speed are needed in LTE-advanced for the next generation mobile communication system. Therefore, spectrum aggregation method has been studied recently to extend usable frequency bands. Also bandwidth utilization is increased since vacant frequencies are used to communicate. However, transceiver structure requires the digital RF and SDR. Therefore, frequency synthesizer and PA must operate over wide-bandwidth and RF impairments also increases in transceiver. Uplink of LTE advanced uses DFT-S OFDM using plural power amplifier. The effect of ICI increases in frequency domain of receiver due to phase noise and IQ imbalance. In this paper, we analyze influences of ICI in frequency domain of receiver considering phase noise and IQ imbalance in multiband system. Also, we separate phase noise and IQ imbalance effect from channel response in frequency domain of uplink system. And we propose a method to estimate the channel exactly and to compensate IQ imbalance and phase noise. Simulation result shows that the proposed method achieves the 2 dB performance gain of BER=$10^{-4}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.467-474
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• 2007

MB-OFDM (Multiband-orthogonal frequency division multiplexing) UWB (ultra wide band) system uses DCM (dual carrier modulation) scheme to achieve high-data rate transmission. The basic idea of DCM is that to transmit the 4 bits more reliably two 16-QAM (quadrature amplitude modulation) symbols are used and the two 16-QAM sysmbols are allocated to each subcarrier of OFDM with maximum-distance. In the case of using the DCM, if one 16-QAM symbol is broken by deep fadding channel, a receiver can detect the transmitted signal by using another 16-QAM symbol. In the conventional ML(maximum likelihood) decision scheme, since the receiver does not use the CSI (channel state information), loss in diversity can not be reduced. In this paper, we propose improved soft-decision scheme with CSI for higher performance of MB-OFDM UWB systemn.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.8
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• pp.125-136
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• 2009

This paper presents a high-speed low-complexity two-bit level pipelined Viterbi decoder architecture for MB-OFDM UWB systems. As the add-compare-select unit (ACSU) is the main bottleneck of the Viterbi decoder, this paper proposes a novel two-bit level pipelined MSB-first ACSU, which is based on 2-step look-ahead techniques to reduce the critical path. The proposed ACSU architecture requires approximately 12% fewer gate counts and 9% faster speed than the conventional MSB-first ACSU. The proposed Viterbi decoder was implemented with $0.18-{\mu}m$ CMOS standard cell technology and a supply voltage of 1.8V. It operates at a clock frequency of 870 MHZ and has a throughput of 1.74 Gb/s.