Tae-Sung Kang

Optimal Beam Subset and User Selection for Orthogonal Random Beamforming

The throughput performance of orthogonal random beamforming (ORBF) with a finite number of users is limited due to the increasing amount of residual interference. In this letter, we find the optimal beam subset, the optimal user set, and the optimal number of random beams to maximize the sum throughput of the ORBF. The proposed scheme provides the best trade-off between the multiplexing gain and the multiuser interference by the determination of the optimal number of random beams as well as the beam selection diversity gain due to the selection of the optimal beam subset. In addition, two efficient suboptimal schemes are presented to reduce the computational complexity and the feedback overhead of the optimal method.

An Efficient Resource Allocation for Multiuser MIMO-OFDM Systems with Zero-Forcing Beamformer

In this paper, a low complexity subcarrier allocation scheme is proposed for multiuser MIMO-multiuser OFDM systems with zero-forcing beamforming (ZFBF) to minimize the total transmit power satisfying given target data rates of users. The ZFBF for multiuser MIMO makes multiple spatial channels by removing multiuser interference and the subcarrier allocation can be performed over spatial and frequency domain. Since the optimal method has very high computational complexity, the semi-orthogonal user selection (SUS) is employed to reduce the computational complexity. In numerical results, we show that the total transmit power satisfying the data rates of users is linearly decreased with the number of transmit antennas.

An Efficient Random Beamforming Method based on Beam Subset Selection

In the finite number of users, the proposed beam subset selection method improves the throughput performance of the orthogonal random beamforming (ORBF), which is a scheme to achieve asymptotic sum capacity for a downlink multiuser multiple-input/multiple output (MIMO) system using partial channel information in the infinite number of users. We show that there exists an optimal number of random beams to maximize the sum throughput for given number of users. When the number of random beams is less than the number of antennas, selecting the random beams to maximize signal- to-interference-plus-noise ratios (SINRs) provides additional SINR gain to ORBF. Through the simulation results, we show the performance improvement by the proposed beam subset selection.

A low complexity blind space-time multiuser detector for multipath fading channel in DS/CDMA systems

In this paper, we propose a low complexity blind space-time multiuser detector for multipath fading channel in DS/CDMA systems. The conventional blind space-time multiuser detector uses MOE (minimum output energy) detectors to suppress interference and MRC (maximum ratio combiner) to obtain spatial and temporal diversity. But this receiver has disadvantage that the number of MOE detectors grows with the number of resolvable multipaths. The proposed space-time multiuser detector reduces the number of detectors using a MV (minimum variance) detection scheme. It is shown that one MV detector has the same performance as many MOE detectors as the number of multipaths. From this result, fewer blind multiuser detectors are required in the proposed scheme. Simulation results show that MV detector has the same performance as MOE detectors with MRC and the proposed scheme exhibits better performance than the conventional scheme.