Jaesang Ham

A practical MMSE-ML detector for a MIMO SC-FDMA system

We propose a new minimum mean square error (MMSE) based maximum likelihood (ML) detector for a single carrier frequency division multiple access system. By utilizing the distance between decision line and MMSE soft-output, the proposed detector reduces the resources required to check superfluously accurate reliability of received symbol. The proposed detector provides almost same bit error rate with the conventional MMSE-ML detector while requiring significantly low computational complexity (below 10%) as SNR varies.

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.

Link-Adaptive MIMO Systems With Ordered SIC Receiver Using Stream-Ordering Algorithms in Multiuser Environments

This paper proposes new algorithms to improve the bit error rate (BER) and data rate of link-adaptive multiple-input-multiple-output (MIMO) systems with ordered successive interference cancellation (OSIC) receivers in a multiuser environment. The proposed algorithms are as follows: (1) the power adaptation (power allocation-equal rate) scheme; (2) the rate adaptation (equal power-adaptive modulation) scheme; and (3) the power and rate adaptation (power allocation-adaptive modulation) scheme. Additionally, as the OSIC receiver is exploited in the proposed algorithms, the detection order of each users receiver is considered since the performance of the system using it is seriously affected by the detection order. Finally, the proposed algorithms are executed to minimize the BER or to maximize the data rate of the system by simultaneously considering link adaptation techniques and the detection order of the OSIC receiver.

An adaptive modulation algorithm for performance improvement of MIMO ML systems

In this letter, we propose a simplified adaptive modulation algorithm for a multiple input multiple output (MIMO) system with a maximum likelihood (ML) receiver to minimize BER under a fixed data rate. The proposed algorithm has the advantages of good system performance and low computational complexity, when compared to previous algorithms.

Performance analysis of a downlink MIMO MC-CDMA system with turbo coding and channel interleaving

In this paper, we pre-sent the multi-code minimum mean square error (MMSE) ordered successive interference canceller (OSIC) for downlink multiple input multiple output (MIMO) multi-carrier code division multiple access (MC-CDMA) systems and analyze its performance from the viewpoint of frame error rate (FER) and data throughput. It outperforms multiuser MMSE OSIC since it can cancel other antenna interference by using all known code information. We make performance comparisons between symbol interleaving before spreading and chip interleaving after spreading in the frequency domain for turbo encoded MIMO MC-CDMA systems. They demonstrate that the chip interleaving method is superior to the symbol interleaving method when the number of multipaths increases owing to the randomization effect of burst errors, and is inferior to the symbol interleaving method when the number of codes increases due to inter-code interference as SISO MC-CDMA systems. Besides, we can derive spatial diversity as well as frequency diversity from multiplexing turbo encoded data streams into transmitting antennas.

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.

Power Control Techniques for Two-Stream MIMO System With Maximum Likelihood Receiver

In this letter, simple power control techniques are proposed to minimize error probability of a two-stream multiple-input multiple-output (MIMO) system with two transmit antennas and a maximum likelihood (ML) receiver, which is known as an optimal receiver but has a high computational complexity problem. The proposed techniques using Euclidean distances of a few error vectors have the advantages of exactly same error performance and very low computational complexity, compared with an optimal power control technique.

Channel-Based Multi-Dimensional Set Partitioning for MIMO Reduced-State Sequence Estimation

A multi-dimensional set partitioning (MDSP) is proposed for reduced-state sequence estimation of multi-path fading multiple input multiple output (MIMO) channels. The proposed MDSP takes channel state information into account when making a set partition because MIMO channels change the distance between symbol vectors in a multi-dimensional constellation. To reduce complexity of the proposed MDSP, we propose an efficient MDSP algorithm which exploits only typical error vectors for partitioning.