So-Young Yeo

Low Complexity ML Detection Technique for V-BLAST Systems with DFE Decoding

In this letter, a low complexity ML detection technique for V-BLAST systems is proposed. In this proposed scheme, V probable streams are detected according to the first detected sub-stream of DFE detector and most probable stream is selected by likelihood test, since the performance of V-BLAST system depends on the first sub-stream detection capability. It has been shown that the proposed technique can detect the transmitted data more accurately than conventional DFE decoding scheme, and has very lower complexity than ML detector.

Efficient techniques in OFDM system with channel evaluation

In this letter, we aim at the study of an OFDM system that employs adaptive modulation techniques to achieve efficient transmission service. In adaptive modulation techniques, a banded AM technique can reduce the number of adaptive modulation information bits and signaling overhead. We evaluate the banded AM technique and compare with Subcarrier AM technique. Moreover, to evaluate the channel condition, we apply the SNR estimation method. Furthermore, to increase the performance of OFDM system, frequency domain pre-equalization is applied. The simulation results have been shown that the OFDM system with adaptive schemes can achieve the efficient transmission for multi-media services.

Cooperative Transmission Technique Using Space Time Delay Code in OFDMA Uplink System

Multiple antennas are used to an essential part in order to support high link quality in wireless communication systems. The diversity techniques with multiple antennas provide better reliability than existing systems. But these techniques generally require more than one antenna at the transmitter or receiver. So, the system with multiple antennas has several limitations including size, cost, hardware complexity, and antenna space. In this letter, we propose a cooperative transmission technique that uses space time delay code in OFDMA uplink system; DVB-RCT. The proposed technique overcomes these limitations and gives the diversity gain of cooperative transmission in a concept of virtual MIMO with single transmit antenna.

Performance analysis of mutual decode-and-forward cooperative communication for OFDMA based mobile WiMAX system

A cooperative communication has been frequently studied because it provides reliability to the previous communication system without the addition of antenna. However, in a cooperative communication, the throughput of the communication system is decreased by half because each station cannot transmit own signal for relaying process. To overcome above limitation and provide more reliability, we propose and analyze the mutual decode-and-forward (DF) cooperative communication for orthogonal frequency-division multiple access (OFDMA) based mobile WiMAX system with single antenna in the Rayleigh fading channel environment. By adopting the proposed scheme, the performance of the mobile WiMAX system is improved in proportion as the quality of inter-user channel is increased.

MB-OFDM UWB system with multiple antennas for high capacity transmission in wireless personal area network

We apply the MIMO layered space-time architecture to MB-OFDM UWB system supporting streaming multimedia content and full motion video in WPAN for low cost and high performance. And also we address a channel estimation based on the time-domain windowing and its imperfectness in MB-OFDM with MIMO antenna systems.

High capacity and reliability techniques for digital audio broadcasting system

Multiple transmitting and receiving antennas can be used in DAB systems to attain high-rate transmission and to offer better quality. In the MIMO-DAB systems, the transmission rate is efficiently increased by the number of antennas. In this paper, we introduce a new channel estimation method using the window function and evaluate the BER performance according to the number of antennas in MIMO-DAB systems. Also an effect of receiver diversity on the performance of MIMO-DAB system is investigated and the achievable receiver diversity gain for a Rayleigh fading environment is evaluated. For effective signal detection, a new detection scheme using interference nulling and cancellation operation is proposed in MIMO-DAB systems. And also we have been shown that the MIMO-DAB system with combining detection can achieve the high-rate transmission for high quality multimedia services.

Flexible and reliable transmission techniques for scale-free UWB system

The speedy dissemination of digital consumer electronics devices within home and personal area causes increments of multimedia communication and advent of entertainment networking. This feature of communication requires variable data-rate and reliable transmission. In order to meet the various demands, in this paper, the multiband orthogonal frequency division multiplexing (MBOFDM) ultra-wideband (UWB) system by exploiting a time domain spreading factor and multiple-access scheme is proposed for variable data-rate transmission from 20kbps to 960Mbps in wireless communication. This article presents the basic structure and main functions of the variable data-rate (VR)-UWB system. With an emphasis on a proposed idea, we address the multiple-access in MB-OFDM system and apply adaptive bit allocation schemes to OFDMA system. It is shown in this article that scale-free UWB can accept multiple users and provide variable data-rate as well as support reliable transmission, while most conventional studies focus on the fixed rate transmission. The proposed system will be promising solution in ubiquitous environment to support multimedia traffic with various rates.

Performance Enhancement Schemes of OFDMA System for Broadband Wireless Access

Orthogonal frequency-division multiple access (OFDMA), which is a combination of orthogonal frequency-division multiplexing (OFDM) with frequency-division multiple access (FDMA), is regarded as a promising solution for enhancing the performance of interactive wireless systems in ubiquitous mobile communication environment. In such an application, this paper presents an investigation into improving the channel estimation scheme and of the effects of symbol timing misalignment when OFDMA is used as an access scheme. Under OFDMA uplink channel environments, appropriate symbol length of CAZAC sequences as a preamble could be utilized in accordance with the number of transmitting antenna and channel condition. The effect of the number of CAZAC sequences for channel estimation is also presented in terms of mean square error (MSE). Taking into account the effect of multiple access interference (MAI) introduced by a symbol timing misalignment, the symbol error rate (BER) and throughput performance are investigated for a typical OFDMA uplink scenario.

Improved and trustworthy detection scheme with low complexity in VBLAST system

We provide a new detection scheme for interference nulling and cancellation operation in a vertical Bell laboratories layered spacetime (VBLAST) system to reduce unexpected effects due to parallel transmission in this paper. This method can reduce the time delay as well as moderate the multipath fading effect. We will show that the performance of investigated VBLAST detection based on hybrid processing performs better than ordinary VBLAST detections based on successive and parallel processing, respectively.

Multi-channel estimation in multiple antenna MB-OFDM UWB system for home entertainment network

The speedy dissemination of digital consumer electronics devices within home and personal area causes increments of multimedia communication and advent of entertainment networking. This feature of communication requires high data-rate transmission. In order to meet the demand, in this paper, a high-speed MB-OFDM system, proposal of 802.15.3a standard for WPAN, employing layered space-time architecture is considered for possible WPAN applications. The MB-OFDM system with multiple antennas increases the transmission rate efficiently with low multiplication operations. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation in MB-OFDM with MIMO antenna system. By properly designing each preamble for multiple antennas to be orthogonal in time domain, the channel estimation can be applied to the MB-OFDM proposal for IEEE 802.15.3a standard in the case of more than two transmitting antennas.