Myung-Sun Baek

Semi-blind channel estimation and PAR reduction for MIMO-OFDM system with multiple antennas

A combining of MIMO signal processing with OFDM is regarded as a promising solution of enhancing the performance of next generation wireless system. Therefore, in this paper, an OFDM-based wireless system employing layered space-time architecture is considered for a high-rate transmission. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in MIMO-OFDM system. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be executed based on semi-blind processing in the case of more than two transmitting antennas. And also we evaluate the PAR performance in the MIMO-OFDM system using the SLM and PTS approaches. The investigated SLM and PTS schemes for MIMO-OFDM signals select the transmitted sequence with lowest average PAR over all transmitting antennas and retrieve the side information very accurately at the expense of a slight degradation of the PAR performance. The low probability of false side information can improve the overall detection performance of the MIMO-OFDM system with erroneous side information compared to the ordinary SLM and PTS approaches, respectively. Also, we provide closed form of the average BER performance in MIMO-OFDM system using analytic approach.

Combined QRD-M and DFE detection technique for simple and efficient signal detection in MIMO-OFDM systems

An efficient MIMO signal detection technique with low complexity is presented for MIMO-OFDM systems. The proposed technique has a feature of combined QRD-M and DFE detection. In our detection technique with M transmit antennas, after QRD-M detection is executed for first T detection steps, DFE detection is executed for last M - T detection steps. This approach is simple and has low complexity, because the computations for QRD-M is limited by the newly adopted parameter T. From simulation results, the complexity of the proposed technique with 4 times 4 and T = 2 is reduced by 61% compared with that of the conventional QRD-M at the expense of about 0.7dB degradation of BER performance at BER=10-4. The simulations are executed in Ricean and Rayleigh channel models. And the simulation of proposed technique is executed by using estimated channel. Through the simulations, it is ascertained that the proposed detection can be used for Ricean and Rayleigh channel models as well as estimated channel.

MULTIPLE ANTENNA TRANSMISSION TECHNIQUE FOR UWB SYSTEM

In this paper, the channel estimation in multi-band OFDM (MB-OFDM) ultra-wideband (UWB) based multipleantenna transmission systems is studied. For multiple antennas, each preamble designed by the Zadoff-Chu sequence satisfies the orthogonal property in the time domain. Therefore, the proposed preambles can improve the system performance and be applied to MB-OFDM specification in the case of more than two transmit antennas.

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.

Multi-antenna scheme for high capacity transmission in the digital audio broadcasting

In this paper, we apply multi-antenna scheme to DAB system for high-rate transmission. In the MIMO-DAB system with a number of transmitting and receiving antennas increases the transmission rate efficiently with low multiplication operations. For channel estimation in the MIMO-DAB system, we propose a new PRS structure and evaluate the channel estimation performance. The proposed PRS structure can estimate multi-channel information based on the semi-blind processing. The performance of proposed PRS is compared with that of conventional training sequence employing Tarokhs transmission matrix. And also we investigate the performance limitation due to the imperfect channel estimation in a MIMO-DAB receiver. It has been shown that the MIMO-DAB system with multi-antennas can achieve the high-rate transmission for multimedia broadcasting and the performance of MIMO-DAB system is impaired by imperfect channel information.

Efficient detection scheme in MIMO-OFDM for high speed wireless home network system

This paper proposes a MIMO-OFDM scheme reducing the computational complexity and providing comparable performance to QRD-M detection scheme in IEEE 802.11n. The proposed scheme checks the channel condition per subcarrier and then selects either ordered DFE scheme or adaptive QRD-M detection scheme according to that information. The post-detection SNR which judges channel condition depends on Moore-Penrose pseudo-inverse matrix G. The proposed scheme selects the ordered DFE detection scheme in case of good channel condition and the adaptive QRD-M detection scheme in case of bad channel condition per subcarrier. The adaptive QRDM detection scheme selects the number of variable survival symbols M in accordance with the channel condition at each layer. Compared with the conventional QRD-M (M=16) detection scheme, the proposed detection scheme reduces the computational complexity about 67 percents and achieves similar performance.

Efficient MIMO Receiving Technique in IEEE 802.11n System for Enhanced Services

A combining of MIMO signal processing with OFDM is regarded as a promising solution of enhancing the performance of next generation WLAN system. Therefore, in this paper, IEEE 802.1 In system employing layered space-time architecture is considered for a high-rate transmission service. However, the IEEE 802.1 In system with V-BLAST scheme has not reached the available capacities due to imperfect nulling and cancellation. In this paper, efficient detection is proposed for IEEE 802.11 n system. In this proposed scheme, T 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 performance of IEEE 802.1 In system can be improved by adopting the proposed detection, and the decoding complexity and system performance can be controlled by adjusting the number of T1.

An Audio Quality Evaluation of Commercial Digital Radio Systems

In this paper, the subjective audio quality of various digital radio systems is evaluated. In order to estimate the true audio quality of a commercial digital radio service, test audio signals were acquired directly from the digital radio equipment in the field. Twenty-one subjects participated in the test after pre-screening. The evaluation process consisted of two phases. In the first phase, the audio quality of each system was evaluated as a function of the bit rates, and the relationship between the audio quality and the channel capacity of each system was obtained. In order to confirm the evaluation consistency, in the second phase, the audio quality as a function of the systems was evaluated. Assuming that the digital radio equipment tested in this paper is used for service, these evaluation results provide the true audio quality of commercial digital radio services for various types of systems and bit rates, and can be used as a reference to determine the optimal channel capacity of digital radio service for a given target audio quality.

Cooperative diversity technique for MIMO-OFDM uplink in wireless interactive broadcasting

OFDMA is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. Recently, to enhance the performance of OFDMA systems, MIMO techniques have been investigated, and the OFDMA systems have been extended to MIMO architectures. Although transmit diversity is clearly advantageous on OFDMA uplink system in interactive broadcasting, it may not be possible that practical OFDMA system of wireless interactive broadcasting have more than two antennas due to size, cost, or hardware limitations. Cooperative diversity techniques are proposed to overcome the limitations. Cooperative networks aim to utilize the available terminals as a collection of distributed antennas for the transmission of signals from one end of the network to the other. Therefore, this paper focuses on design and performance evaluation of MIMO-OFDMA uplink system with cooperative diversity for wireless interactive broadcasting. For high-rate and reliable transmission, efficient transmission codes are proposed for two transmission cases (one-sided transmission case and two-sided transmission case). And, we present our investigations of the effects of line-of-sight. In the wireless communication environment, line-of-sight is very important to improve the system performance. Under the condition of utilizing the line-of-sight of cooperative partner, the performance of a terminal without line-of-sight can be improved. Taking into account the effects of utilizing line-of sight of cooperative partner, the BER performance is investigated for a MIMO-OFDMA uplink scenario.

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.