Hui Won Je

A novel uplink MIMO transmission scheme in a multicell environment

Uplink multiple-input multiple-output (MIMO) transmission scheme is developed for time division duplex (TDD) systems in a multicell environment. We propose a precoding scheme that maximizes the total achievable rate and works in the decentralized manner with only locally available channel state information (CSI) at each transmitter. We first establish and solve a decentralized optimization problem for the case of multiple-input single-output (MISO) channels, introducing a new precoding design metric called signal to generated interference plus noise ratio (SGINR). By extending the result to general MIMO channels, we propose an SGINR-based precoding scheme where the number of transmit streams is selected adaptively to the surrounding environments. Simulation results confirm that the proposed precoding scheme offers significant throughput enhancement in multicell environments.

A novel multiple access scheme for uplink cellular systems

A novel multiple access scheme for the uplink cellular systems, referred to as FH/SS-OFDMA, is proposed. The proposed scheme employs both frequency hopping and code multiplexing on the frequency domain to acquire frequency diversity and suppress intercell interference. The performance of the proposed scheme is investigated and evaluated in cellular environments and compared with that of other multiple access schemes. It has been found that the proposed one outperforms other multiple access schemes. Simulation results for various parameters, such as system load, modulation scheme, spreading factor, and interference level are also presented.

Interference-Aware Decentralized Precoding for Multicell MIMO TDD Systems

Multiple-input multiple-output (MIMO) precoding scheme is developed for time division duplex (TDD) systems in a multicell environment. The proposed scheme is designed to maximize the total achievable rate, and to work in the decentralized manner with only locally available channel state information (CSI) at each transmitter. We first establish and solve a decentralized optimization problem for the case of multiple-input single-output (MISO) channels. We introduce a new precoding design metric called signal to generating interference plus noise ratio (SGINR). Based on the SGINR metric, the MISO precoding scheme is extended to general MIMO channels. Simulation results confirm that proposed precoding scheme offers significant throughput enhancement in multicell environments.

Design of Non-Regenerative MIMO-Relay System with Partial Channel State Information

Design strategy for non-regenerative multiple-input multiple-output (MIMO) relay system with partial channel state information (CSI) is developed. We assume that the CSI of the base station-relay link is fully known to the relay, while the CSI of the relay-mobile station link is not known except its channel statistics. Based on this model, weighting matrices to increase ergodic capacity is proposed for downlink and uplink MIMO-relay system, respectively, with the approximation for both the high and low signal-to-noise ratio (SNR) region. We also propose a switching scheme to cover the intermediate SNR region. Numerical results show that the proposed scheme outperforms the conventional one especially when the SNR becomes high.

Joint Precoding for MIMO-Relay Systems with Partial Channel State Information

In this paper, we propose a joint precoding scheme for both the base station (BS) and relay station (RS) to increase the ergodic capacity of downlink non-regenerative multiple-input multiple-output(MIMO)-relay systems. Different from previous work, we assume only the mean and the covariance matrix are known for the channel state information (CSI) of the RS-mobile station(MS) link. Since the exact solution of this problem is difficult to be found because the RS-MS channel is only partially known, we employ precoding matrices that maximize the upper bound on the ergodic capacity. Based on this approach, the proposed scheme uses an iterative method to determine both BS and RS precoding matrices simultaneously. In numerical results, the proposed joint precoding scheme is shown to outperform the water-filling and amplify-and-forward (WF-AF) scheme in high signal-to-noise ratio (SNR) regions. It is also shown to outperform the spatial multiplexing and RS precoding (SM-RP) scheme in low SNR regions.

Transmit Antenna Subset Selection for Downlink MIMO Systems in Multicell Environments

This letter proposes a statistical cooperative scheme for transmit antenna subset selection in multiple-input multiple-output (MIMO) multicell systems. The proposed scheme is practical in that it only utilizes the statistical information for the adjacent links. However, it provides almost 90 percent of the average mutual information of the full cooperative scheme which requires a large amount of the instantaneous information and joint cooperation between base stations. Furthermore, the proposed scheme shows substantial performance enhancements over the competitive scheme in which the effects of intercell interference generated by the antenna selection are not considered.

Transmit Antenna Subset Selection for Downlink MIMO Systems

This paper discusses transmit antenna subset selection schemes for downlink closed-loop multiple-input multiple-output (MIMO) systems in multicell environments. A simplified cooperative scheme is proposed to increase the sum of the mutual information of the links in all cells. The proposed simplified-cooperative scheme is realistic in that it only utilizes a limited amount of information from adjacent links, while the conventional cooperative scheme requires a large amount of information such as channel state information and MIMO transmit configurations of adjacent links. In spite of the use of a limited amount of information, the proposed scheme provides almost 90 percent of the average mutual information provided by the cooperative scheme. Furthermore, the proposed scheme shows significant enhancements over the competitive scheme which does not consider the effects of antenna subset selection on the performance of adjacent links.

Acquisition for DS/CDMA systems with multiple antennas in frequency-selective fading channels

A code acquisition scheme is proposed for DS/CDMA systems with multiple antennas. The proposed scheme employs a new search scheme, referred to as sparse search, to utilize multipath signals in reducing mean acquisition time over frequency-selective fading channels. The mean acquisition time performance of the proposed scheme is analyzed and evaluated in frequency-selective Rayleigh fading channels. The performance of the proposed scheme is compared with that of the conventional one. Numerical results show that the proposed acquisition scheme outperforms the conventional one, and that the performance improvement becomes greater as the number of resolvable paths increases. The effects of configuration of multiple antennas and receiver complexity on mean acquisition time are also investigated.