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

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.246-252
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• 2012

STBC is a technique where a multiple antenna signals are transmitted. With this technique, antenna diversity can be achieved. The performance of STBC OFDM system using pilot symbol for the channel estimation is analyzed. IEEE 802.16e standards suggest that the BER performance of STBC system can be improved using channel state information. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of this STBC OFDM systems using channel state information, gauged by the average bit error rate, is analyzed considering the channel estimation error.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.950-957
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• 2007

In this paper, a recursive intercarrier interference (ICI) cancellation technique for cooperative space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) with different carrier frequency offsets (CFOs) is proposed. Also, different CFOs existing in a cooperative STBC-OFDM system is shown to produce phase difference in the received signal, causing noise enhancement effect in the STBC decoding process. The performance degradation caused by the noise enhancement effect can be effectively reduced by a proposed ML-based recursive ICI cancellation technique. It is shown by computer simulation that the proposed recursive ICI cancellation technique is effective in reducing ICI, especially for STBC-OFDM systems with a large FFT size and large CFOs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5C
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• pp.391-397
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• 2005

Since space time block code (STBC) technique of a transmission diversity technique was introduced, multiple input multiple output techniques using transmission diversity at the basestation for improving transmission data rate, have been studied extensively. Multiplexed STBC OFDM technique uses multiple groups of two transmit antennas and suppresses the interference signals of other STBC OFDM groups at the receivers. In this paper, I propose a new method of iterative decoding and maximal ratio receive combining technique for multiplexed STBC OFDM systems, and simulated and showed the results in comparison with the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1147-1158
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• 2004

In this paper we design STBC-OFDM systems by applying several STBC schemes to the OFEM system and show their comparative analysis results obtained through computer simulations under Rayleigh fading environments, considering the effect of channel estimation error. We first consider the space-time coding algorithms of major STBC schemes, together with their demodulation algorithms. We then select the OFDMparameters considering mobile environments and design the STBC-OFDM systems by choosing one of digital modulation schemes such as QPSK, BPSK, 16QAM, 64QAM, and 256QAM according to the transmission rate, and describe the block diagrams of the demodulator and channel estimator. We finally compare and analyze the BER performances of the STBC-OFDM systems according to the transmission rate and the number of receive antennas.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.240-247
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• 2004

In order to transmit data at high speed in the wireless environment, OFDM is selected as the transmission method of various high-speed wireless communication system since it has the advantage to deal easily the serious selective frequency fading channel by the multiple path. We evaluate STBC-OFDM and linear STBC-OFDM combining with a class of recently proposed linear scalable space-time block codes and OFDM in MIMO channel environments, and demonstrate the performance for spatial multiplexing and diversity gain. The codes are able to use jointly transmit diversity in combination with spatial multiplexing, and achieve spatial and temporal diversity. Frequency diversity of frequency selective channels can be utilized by combining the linear STBC and OFDM. Simulation results are shown to demonstrate the better performance of proposed approach in comparison with STBC-OFDM.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.18-26
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• 2006

In this paper, we compare the performance of three representative STBC schemes, Alamouti's, Tarokh's and quasi-orthogonal schemes under cellular mobile environments when they are applied to the OFDM system. We first study the encoding algorithms of the STBC schemes along with the development of adequate demodulation algorithms. The OFDM parameters are selected by considering the Wibro system and adequate modulation schemes are assigned for each STBC schemes according to the transmission rate from 2bps/Hz to 4bps/Hz. The STBC-OFDM systems employ Walsh orthogonal codes covered along the frequency domain in order to estimate the channel information for different transmit antennas. We finally compare the performance of the STBC-OFDM systems according to the transmission rate through computer simulations in various mobile channel environments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.12
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• pp.8-16
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• 2010

In this paper, we present a structure of computationally efficient MIMO-OFDM transmitters, using STBC. Straightforward implementation of these systems requires separate WFT processing blocks for each of the transmit antennas. In our proposed scheme, we use symmetry properties of Fourier transform, and thus use a frequency domain encoding strategy. This greatly reduces the computational burden. The proposed scheme uses just a single IFFT block at each OFDM symbol period, and thus resulting in the same complexity as a single antenna OFDM system. As specific examples of the proposed schemes, we present frequency domain encoding matrices for QO-STBC-OFDM and QO-SFBC-OFDM transmitters.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.144-154
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• 2004

In this paper we apply the space-time block codes (STBCs), the key technologies for the 4th generation mobile communication systems, to the OFDM system and analyze their performances. First, we derive the signal models for representative STBC schemes and demodulation procedures for each scheme. We also select the parameters for OFDM system considering mobile cellular environments and assign adequate modulation schemes to STBC-OFDM schemes according to the transmission rate from 2bps/Hz to 4bps/Hz. We finally compare and analyze the performances of STBC-OFDM schemes for the selected transmission rates through computer simulations, together with performance comparison when the same modulation scheme being adopted.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.351-358
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• 2005

In this paper, STBC(Space Time Block Code) is applied to the UWB system and frequency repeated diversity is used to get the 4-th order space time diversity gain. The performance of UWB STBC-OFDM system is analyzed by computer simulation. As a result of analysis, proposed UWB system can reduce the complexity that is introduced by increaing number of radiator and show the same performance of 4 antennas with that only using 2 radiator. This system at the $10^{-4}$ also shows the enhancement of $7.1\;\cal{dB}$ to the general UWB OFDM and $1.9\;\cal{dB}$ to UWB STBC-OFDM.