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

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.9
• /
• pp.1-8
• /
• 2007

In this paper, the new beamforming is proposed for an orthogonal frequency division multiplexing(OFDM) system with multi-input multi-output(MIMO). Through the proposed Pre-FFT beamforming technique for MIMO-OFDM, the multibeams are formed toward each multi-transmitter antenna of the desired user. The proposed beamforming for MIMO-OFDM can reduce cochannel interference and get diversity gain in the multi-user environment. Therefore, the performance of MIMO-OFDM system is very improved. BER performance improvement of the proposed approach is investigated through computer simulation by applying it to MIMO-OFDM system in the multi-user environment.

• ETRI Journal
• /
• v.26 no.6
• /
• pp.565-574
• /
• 2004

Differential unitary space-time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with frequency-selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO-OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.10
• /
• pp.2275-2284
• /
• 2015

In this paper, the Walsh coded orthogonal training signals for 4 × 4 multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems are designed and the channel estimation equations are derived as a closed form, taking account of the inter training signal interference problems caused by the multi-path delayed signals. The performances of the proposed channel estimation method are analyzed and compared with the conventional methods[9,14] by using computer simulation. The simulation results show that the proposed methods has better performances, compared with the conventional methods[9,14]. As a result, the proposed method can be used for MIMO-OFDM systems with null sub-carriers.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11A
• /
• pp.1027-1037
• /
• 2010

In this paper, we propose the linear interpolation-based BD (Block Diagonalization) precoding approximation algorithm for low complexity in downlink multiuser MIMO-OFDM (Multiple-input Multiple-output Orthogonal Frequency Division Multiplexing) systems. In the case of applying the general BD precoding algorithm to multiuser MIMO-OFDM systems, the computational complexity increases in proportional to the number of subcarriers. The proposed interpolation-based BD precoding approximation algorithm can be achieved similar SER performance with general BD algorithm and can decrease the computational complexity. It is proved that proposed algorithm can achieve the significantly decreased computational complexity by computer simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.12
• /
• pp.3200-3219
• /
• 2013

This paper proposes an adaptive combined scalable video coding (CSVC) system for video transmission over MIMO-OFDM (Multiple-Input Multiple-Output-Orthogonal Frequency Division Multiplexing) broadband wireless communication systems. The scalable combination method of CSVC adaptively combines the medium grain scalable (MGS), the coarse grain scalable (CGS) and the scalable spatial modes with the limited feedback partially from channel state information (CSI) of MIMO-OFDM systems. The objective is to improve the average of peak signal-to-noise ratio (PSNR) and bit error rate (BER) of the received video stream by exploiting partial CSI of video sources and channel condition. Experimental results show that the delivered quality using the proposed adaptive CSVC over MIMO-OFDM system performs better than those proposed previously in the literature.

• Proceedings of the IEEK Conference
• /
• 2003.11a
• /
• pp.545-548
• /
• 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
• /
• 2003.11c
• /
• pp.204-207
• /
• 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.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.5
• /
• pp.18-24
• /
• 2010

This paper propose a dual-layer beam-forming technique for MIMO-OFDM systems. Dual-layer beam-forming is a capacity enhancing technique to transmit two streams of source data with more than two transmit and receive antennas. Beamforming is a technique to enhance the link-level performances gain using antenna array with the small inter element distance. The proposed scheme can obtain both high capacity of spatial multiplexing and antenna array gain of beamforming for MIMO-OFDM systems. Therefore, it provides better BER performance than the traditional spatial multiplexing and beamforming techniques under the same simulation environment.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.6A
• /
• pp.563-574
• /
• 2006

This paper implements SCM(Spatial Channel Model), a kind of ray-tracing method which has characteristics similar to realistic wave propagation environments, for link-level performance analysis of OFDM(Orthogonal Frequency Division Multiplexing) based multiple antenna systems. The SCM is proposed by 3GPP & 3GPP2 Spatial Channel AHG(Ad-hoc Group) for system-level performance validation. In this paper, we modify the system level parameters and channel coefficient of SCM to compare the link-level performances of OFDM based multiple antenna systems. Through computer simulations, we manifest the implemented SCM channel characteristics. We analyze a realistic link-level performance of OFDM based conventional MIMO(Multiple Input Multiple Output) system and smart antenna system in the implemented channel. We also include the link-level performance of OFDM based multiple antenna systems in I-METRA(Intelligent Multi Element Transmit and Receive Antenna) and independent channel environments with the same system parameters. We suggest appropriate multiple antenna system in the given environment by comparing the link-level performance in the spatial channels that have different channel correlation values.