• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.568-573
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• 2002

In this paper, the Viterbi decoder containing new branch metrics of the squared Euclidean distance with multiple order phase differences is introduced in order to improve the bit error rate (BER) in the differential detection of the trellis-coded MDPSK-OFDM. The proposed Viterbi decoder is conceptually same as the Continuous multiple phase differential detection method that uses the branch metric with multiple phase differences. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency Also. the proposed algorithm ran be used in the single carrier modulation.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.277-279
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• 2004

In this paper, we propose an channel estimation method for Multi-Input Multi-Output-Orthogonal frequency Division Multiplexing (MIMO-OFDM). The proposed method estimates uniquely all channel frequency responses needed in space-frequency block coded OFDM systems using "comb-type" pilot symbols. To reduce the computational complexity of the proposed method, least square(LS) and linear minimum mean square error(LMMSE) are used in the frequency-domain. The performance of the proposed approach is evaluated by computer simulation for rayleigh fading channel.

• Proceedings of the IEEK Conference
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• 2003.11a
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• pp.545-548
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• 2003

MIMO-OFDM 시스템은 다중 안테나 송신을 통하여 시스템의 capacity를 극대화 하지만, 이를 위해서는 정확한 채널계수 값의 추정을 필요로 한다. 본 논문에서는 MIMO-OFDM시스템을 위한 채널계수 추정기법으로서 Space-Time Coding(STC)에 기반을 둔 방식을 제안한다. 제안된 채널 계수 추정 기법을 위해 필요한 심볼 구조, frame 구조를 IEEE 802.11a 시스템에 적용하였다. VBLAST 기법이 적용된 IEEE 802.11a 기반의 4 by 4 MIMO-OFDM 시스템에 대한 모의 실험을 통하여 제안된 방법의 성능과 기존의 방법의 성능을 coded BER를 통해 비교 분석해 보았다.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.204-207
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• 2003

MIMO-OFDM 시스템은 다중 안테나 송신을 통하여 시스템의 capacity를 극대화하지만, 이를 위해서는 정확한 채널 계수 값의 추정을 필요로 한다. 본 논문에서 는 MIMO-OFDM 시스템을 위한 채널계수 추정기법으로서 Space-Time Coding(STC)에 기반을 둔 방식을 제안한다. 제안된 채널계수 추정기법을 위해 필요한 심볼구조, frame 구조를 IEEE 802.11a 시스템에 적용하였다. VBLAST 기법이 적용된 IEEE 802.11a 기반의 4 by 4 MIMO-OFDM 시스템에 대한 모의실험을 통하여 제안된 방법의 성능과 기존의 방법의 성능을 coded BER를 통해 비교 분석해 보았다.

• ETRI Journal
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• v.26 no.5
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• pp.384-390
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• 2004

We propose a new bandwidth-efficient technique that achieves high data rates over a wideband wireless channel. This new scheme is targeted for a multiple-input multiple- output orthogonal frequency-division multiplexing (MIMO-OFDM) system that achieves transmit diversity through a space frequency block code and capacity enhancement through the iterative joint processing of zero-forcing detection and maximum a posteriori (MAP) decoding. Furthermore, the proposed scheme is compared to the coded Bell Labs Layered Space-Time OFDM (BLAST-OFDM) scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5A
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• pp.436-444
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• 2005

Unitary matrix modulation (UMM) is investigated in multiple antennas system that is called unitary space-time modulation (USTM). In an OFDM, the diagonal components of UMM with splitting over the coherence bandwidth (UMM-S/OFDM) have been proposed. Recently LDPC code is strongly attended and studied due to simple decoding property with good error correction property. In this paper, we propose LDPC coded UMM-S/OFDM for increasing the system performance. Our proposed system can obtain frequency diversity using UMM-S/OFDM like USTM/OFDM, and large coding gain using LDPC code. The superior characteristics of the proposed UMM-S/OFDM are demonstrated by extensive computer simulations in multi-path Rayleigh fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.107-114
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• 2008

In wireless access systems, there has been much interest in enhancing the performance of orthogonal frequency division multiplexing OFDM) in a frequency selective fading channel. If the channel is static and is perfectly known to both the transmitter and the receiver, the water-filling technique with adaptive modulation is known to be optimal. However, for OFDM systems, this requires intensive traffic overheads for reporting channel side information on all subcarriers to the transmitter In this paper, we propose an adaptive modulation and coding scheme for bit-interleaved coded OFDM (BIC-OFDM) for downlink packet transmissions with reduced feedback information. To minimize the feedback information, we employ a rate adaptation method based on the OFDM symbol rather than on each subcarrier. To illustrate the performance gap between the optimal water-filling and the proposed scheme, we will compare cutoff rates for both schemes. It is shown that the loss is less than 2dB while the proposed scheme significantly reduces the feedback payloads. Also, the OFDM system in multiuser environment with subcarrier grouping is considered. It is shown that by exploiting multiuser diversity the throughput of the proposed scheme approaches the channel outage capacity as the number of users and the number of subcarrier groups increase.

• Journal of Broadcast Engineering
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• v.16 no.2
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• pp.226-236
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• 2011

In this paper, we propose the channel estimation for the space time coded-orthogonal frequency division multiplexing (ST-OFDM) muti-input multi-output (MIMO) system with comb type pilot arrangements. In the conventional method, specially constructed pilots are inserted in the OFDM symbols at all transmit antennas separately. The proposed algorithm multiplies the orthogonal code to be transmitted OFDM symbols to estimate channels at the receiver. This algorithm can estimate a long channel delay with high accuracy. It is proved by computer simulations.

• The KIPS Transactions:PartC
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• v.13C no.1 s.104
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• pp.75-82
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• 2006

In this paper, a space-frequency coded orthogonal frequency division multiplexing (SFC-OFDM) scheme with dual Viterbi decoder is proposed and analyzed. Here, two independent half-rate OFDM symbols are generated after convolutional coding of the binary source code. A dual Viterbi decoder is exploited to decode the demodulated sequences independently in the receiver, and their path metrics are compared. Accordingly, the recovered binary data in the proposed scheme are composed of the combination of the sequences having larger path metrics while those in a conventional system are simply the output of single Viterbi decoder. As a result, the proposed SFC-OFDM scheme has a better performance than the conventional one for all signal-to-noise power ratio.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.12
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• pp.28-33
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• 2007

We present a space-time trellis coded OFDM system in flow fading channels. Generalized principal ratio combining (GPRC) is also analyzed theoretically in frequency domain. The analysis show that the decoding metric of GPRC include the metrics of maximum likelihood (ML) and PRC. The computer simulations with M-PSK modulation are obtained in frequency flat and frequency selective lading channels. The decoding complexity and simulation running times are also evaluated among the decoding schemes.