• Journal of Advanced Navigation Technology
• /
• v.8 no.1
• /
• pp.10-18
• /
• 2004

As a technique for high-quality multimedia service in down-link, the transmit diversity schemes using a orthogonal space-time block codes were proposed. But if the number of transmit antenna is three or more, it was impossible to obtain full diversity gain because of the decline of spectral efficiency. Accordingly, the quasi-orthogonal space-time block code that not required a additional bandwidth was proposed. But using a space-time block codes, the transmit diversity schemes were verified over quasi-static and frequency non-selective channels. Therefore, in this paper, we analyze the performance of OFDM systems, which a frequency selective channel equalized a frequency non-selective channel, adapting the quasi-orthogonal space-time block code, and compare they to the conventional orthogonal space-time block coded OFDM systems.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.1
• /
• pp.141-150
• /
• 2010

In this paper, performance of a turbo-coded OFDM system is analyzed and simulated in a power line communication channel. Since the power line communication system typically operates in a hostile environment, turbo code has been employed to enhance reliability of transmitted data. The performance is evaluated in terms of bit error probability. As turbo decoding algorithms, MAP (maximum a posteriori), Max-Log-MAP, and SOVA (soft decision viterbi output) algorithms are chosen and their performances are compared. From simulation results, it is demonstrated that Max-Log-MAP algorithm is promising in terms of performance and complexity. It is shown that performance is improved 3dB by increasing the number of iterations, 2 to 8, and interleaver length of a turbo encoder, 100 to 5000. The results in this paper can be applied to OFDM-based high-speed power line communication systems.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.9C
• /
• pp.896-905
• /
• 2009

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verwey that the proposed method has better performance with approximately same complexity compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.11A
• /
• pp.1092-1100
• /
• 2006

In this paper, we propose a full rate quasi-orthogonal space-time-frequency block coded orthogonal frequency division multiplexing(QOSTF-OFDM) that can achieve full symbol rate with four transmit antennas. Sincr: the proposed QOSTF-OFDM can not achieve full diversity, we use diversity advantage collection with zero forcing (DAC-ZF) decoder to compensate the diversity loss at receive side. At the same frequency efficiency, compared with linear orthogonal space-time codes which can not achieve full rate with four transmit antennas over complex constellations, low level modulation can be employed by proposed scheme due to its full rate, i.e., modulation advantage can be achieved. Due to modulation advantage and collected diversify advantage, the proposed scheme exhibits better BER performance than other orthogonal schemes.

• Proceedings of the IEEK Conference
• /
• 2002.07b
• /
• pp.1066-1069
• /
• 2002

Orthogonal frequency division multiplexing (OFDM) is a special technique for communication systems which can support the high data rate transmission with sufficient robustness to fading channels. Tansmitter diversity with space-time block coding (STBC) is an attractive transmission scheme to improve the performance of systems. In this paper, we compare the performance of space-time block coded OFDM systems with that of conventional OFDM systems over fast fading channels. The block-interleaved (BI) STBC and frequency hopping (FH) OFDM are proposed in the study to provide the maximum achievable diversity gains. As the simulation results, the STBC OFDM, Bl-STBC OFDM and Bl-STBC FH-OFDM provide the much improved performance over the conventional OFDM. And the Bl-STBC FH-OFDM also provide the better performance than the STBC OFDM and Bl-STBC OFDM, especially, in the case of the two transmit antennas are employed while BI-STBC FH-OFDM can maintain the same data rate of 12 Mbps.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.5C
• /
• pp.469-477
• /
• 2007

Most multimedia source coders exhibit unequal bit error sensitivity. Efficient transmission system design should therefore incorporate the use of matching unequal error protection (UEP). In this paper, we present and evaluate a flexible space-time coding system with unequal error protection. Multiple transmit and receive antennas and bit-interleaved coded modulation techniques are used combined with rate compatible punctured convolutional codes. A near optimum iterative receiver is employed with a multiple-in multiple-out inverse mapper and a MAP decoder as component decoders. We illustrate how the UEP system gain can be achieved either as a power or bandwidth gain compared to the equal error protection system (EEP) for the identical source and equal overall quality for both the UEP and EEP systems. An example with two/three transmit and two receive antennas using BPSK modulation is given for the block fading channel.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.38 no.11
• /
• pp.19-29
• /
• 2001

The Pan-European Digital Audio Broadcasting(DAH) system's performance is characterized and improved with the aid of turbo codec. From the fact that the first bit among the four coded bits at the RCPC coding defined in the Eureka 147 DAD system is not. punctured and always transmitted, this paper proposes a new turbo coded DAB system model that replaces the existing RCPC codec by a turbo codec without modifying the puncturing procedure and puncturing vectors defined in the standard DAB system for compatibility. The performance of a new system is compared to that of the conventional system under the Rician fading channel and the Rayleigh fading channel in conjunction with DAD transmission mode I and III suitable for the terrestrial single frequency network and satellite broadcasting.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.8
• /
• pp.1643-1648
• /
• 2005

MIMO system takes advantage of the spatial diversity obtained by spatially separated antennas for high- performance and high-capacity broadband wireless access. In this paper, we propose Carrier Interferometry coded MIMO-OFDM system (MIMO-CI/OFDM) which provides frequency and spatial diversity. One combined diversity gains featly improve the performance of OFDM systems. To perform a performance analysis, we have used SPW platform that provides an easy tool to analyze the performance. The results show that the performance of MIMO-CI/OFDM shows an approximately 4dB gain over the MIMO-OFDM even in highly frequency selective fading channels.

• ETRI Journal
• /
• v.36 no.5
• /
• pp.783-790
• /
• 2014

In this paper, we first analyze carrier-to-interference ratio performance of the space-frequency block coded orthogonal frequency-division multiplexing (SFBC-OFDM) system in the presence of phase noise (PHN) and residual carrier frequency offset (RCFO). From the analysis, we observe that conventional SFBC-OFDM systems suffer severely in the presence of PHN and RCFO. Therefore, we propose a new inter-carrier interference (ICI) self-cancellation method - namely, ISC - for SFBC-OFDM systems to reduce the ICI caused by PHN and RCFO. Through the simulation results, we show that the proposed scheme compensates the ICI caused by PHN and RCFO in Alamouti SFBC-OFDM systems and has a better performance than conventional schemes.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.5A
• /
• pp.402-406
• /
• 2005

A multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system using low-density parity-check (LDPC) code and iterative decoding is presented. The iterative decoding is performed by combining the zero-forcing technique and LDPC decoding through the use of the 'turbo principle.' The proposed system is shown to be effective with high order modulation and outperforms the space frequency block code (SFBC) method with iterative decoding.