Seijoon Shim

An efficient antenna shuffling scheme for a DSTTD system

A new antenna shuffling scheme for DSTTD (double space time transmit diversity) is proposed. The proposed method obtains the shuffling pattern directly from the estimated channel by maximizing minimum post-processing SNR (signal to noise ratio), while the conventional method minimizes channel correlation. Since the minimum post-processing SNR is directly related with error performance, the proposed method shows better bit error rate performance than the conventional method.

A simplified adaptive modulation scheme for D-STTD systems with linear receivers

In this letter, we consider D-STTD (Double Space Time Transmit Diversity) with an adaptive modulation (AM) scheme. The simple criteria for AM are proposed according to linear receivers and the corresponding AM schemes are derived to minimize bit error rate under the constraint of the total data rate and total transmit power. The D-STTD system using the proposed AM scheme requires low computational complexity and small feedback information. The performance of D-STTD system using the proposed scheme is improved by 7 dB or more in signal to noise ratio corresponding to 10/sup -4/ bit error rate.

Rank adaptive transmission to improve the detection performance of the BLAST in spatially correlated MIMO channel

Previous results of information theory have shown that the capacity potential of MIMO wireless communication systems is very large, assuming that the channel matrix, the transfer function between the Tx and Rx antenna pairs, is statistically independent. Though the BLAST has been proposed to use this potential, BER performance and capacity of the BLAST become degraded as spatial correlation increases. The proposed RAT (rank-adaptive transmission) can improve the performance of the BLAST under the Ricean channel model. Its key idea is to control the transmit data rate adaptively according to the estimated channel condition. The computer simulations showed the RAT works well even though the spatial correlation increases.

Asymptotic Analysis of Downlink MIMO Multicarrier CDMA systems with a Minimum Mean Square Error Receiver

This paper analyzes the output signal-to-interference-plus-noise ratio (SINR) for a multiple-input multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) system with minimum mean square error receivers. Previous work on a single antenna MC-CDMA system is based on convergence of the limiting spectral distribution of large dimensional sample covariance matrices and the asymptotic freeness between random matrices. These concepts cannot directly be applied to a MIMO MC-CDMA system because some assumptions for single antenna do not match the case of multiple antenna. Therefore, this paper expands the concept of convergence and freeness to MIMO system by using extended Haar unitary random matrix and the Marcenko-Pastur law. The analysis shows that the output SINR asymptotically converges to a deterministic value with a closed form expression. The analysis is used to obtain improved bit error rate calculation as verified by simulations

An Efficient Adaptive Modulation Algorithm for D-STTD System

In this paper, we consider double space time transmit diversity (D-STTD) with an adaptive modulation (AM) algorithm. The simple criteria to use AM algorithm and antenna shuffling pattern are proposed according to linear receivers such as zero-forcing and minimum mean square error receiver. The AM algorithms are derived to minimize bit error rate (BER) under the fixed total data rate and total transmit power. The D-STTD system using the proposed algorithms requires low computational complexity and small feedback information bits. The performance of D-STTD system using the proposed algorithm is improved by about 5.8 dB or more in signal to noise ratio (SNR) corresponding to 10-3 BER. Additionally, using antenna shuffling, BER performance is more improved, but more feedback information bits are also required.

A new multiuser diversity scheme exploiting detection order for AM-OSIC system

We propose a new detection ordering scheme and multiuser diversity scheme, which minimizes an average error rate occurring in a MIMO system using only adaptive modulation technique applied to an ordered successive interference canceller (OSIC). We simplify an optimal scheme in the view point of error rate by using approximated error rate. Though the complexity is reduced by only maximizing a minimum equivalent SINK, scaled by modulation indices, the simplified scheme demonstrates the almost same performance as the optimal scheme. Owing to the selection diversity of detection ordering, the proposed scheme produces over 3 dB SNR gain at the BER of 10/sup -3/ than the existing ordering schemes in the case of the 2/spl times/2 MIMO system with small amount of feedback information. We also propose the multiuser diversity scheme based on the proposed detection ordering scheme to improve average error rate of multiuser system. Here, multiuser diversity gain is obtained from the effect of user selection by the proposed scheme.

The projection matrix method for interference cancellation

A new method to calculate a weight vector of a beamformer called the projection matrix method, is proposed. The method calculates a projection matrix composed of the steering vector of interference or desired signal, and obtains a new spatial covariance matrix by projecting the signal covariance matrix onto the projection matrix. Then, the method finds the eigenvector corresponding to the largest eigenvalue of the new spatial covariance matrix. If this eigenvector is adopted as a weight vector of a beamformer it is the optimal solution to maximize signal to interference plus noise ratio without requiring the inversion of the covariance matrix. The computer simulations showed that the proposed method effectively design a beamformer to cancel or attenuate interferences.

A Simplified Ordering Scheme Minimizing Average BER for MIMO Systems with Adaptive Modulation

This paper proposes a new detection ordering scheme, which minimizes average error rate of the MIMO system with per antenna rate control. This paper shows an optimal scheme minimizing average error rate expressed by the Q function, and simplifies the optimal scheme by using the minimum equivalent SINR scaled by modulation indices, based on approximated error rate. In spite of reduced complexity, the simplified scheme demonstrates the almost same performance as the optimal scheme. Owing to the diversity of detection ordering, the proposed scheme has over 2 dB higher SNR gain at the BER of 10 -3 than the existing ordering schemes in balanced array size systems.

Low complexity optimal interference rejection weight for multipath interference canceller

Though multicode approach is a popular method for high data rate transmission, multipath interference gives bad effect on high data rate systems, because high level modulation is very vulnerable to multipath interference. To suppress this interference, the parallel type multistage interference canceller (MSIC) is known to be suitable in practical implementation point of view. In the parallel type MSIC, the accuracy of regenerated interference replica has a direct influence on the system performance. In this paper, we derive a low complexity optimal mutlipath interference rejection weight for parallel type multistage partial multipath interference canceller using minimum mean square error criterion based on time multiplexed pilot channel. We observed that the optimal rejection weight varies adaptively according to time-varying Rayleigh fading channel and showed that it has comparable performance with the experimentally obtained optimal weight in the previous work by computer simulation.