Seung-Hoon Hwang

A hybrid ARQ scheme with power ramping

We propose and analyze a scheme for wireless channels, which is a combination of a hybrid type I automatic repeat request (ARQ) scheme and a power ramping. In the hybrid type I ARQ scheme, the same redundancy bits for error correction is transmitted repeatedly when a negative acknowledgment (NAK) is obtained. In addition to the ARQ scheme, the power ramping is considered for more reliable downlink data transmission, in which the transmission power is gradually changed from a small level to large levels when the number of retransmission increases. This is done without any knowledge of the channels at the transmitter. Simulation results show that by applying the combined hybrid ARQ and power ramping scheme with properly selected parameters, it has a throughput advantage of 3-5%.

A Novel Antenna Allocation in V-BLAST System with Hybrid ARQ

In this paper, an efficient algorithm of finding an antenna switching function is proposed for an antenna-switching scheme in vertical Bell Labs layered space-time (V-BLAST) with hybrid automatic repeat request (H-ARQ). The transmit antenna is switched for each retransmission, where the switching pattern is obtained by the criterion of maximizing the channel capacity. The size of search space in the algorithm is not dependent on the maximum number of transmission but only on the number of transmit antennas. From simulation results, the obtained antenna switching function is dependent on channel correlation characteristics. In addition, the SNR values give little impact on the antenna switching function. Simulation results demonstrate that the average throughput can be further improved by the antenna switching function in a correlated fading channel, without adding much complexity to the process.

Impact of the Antenna Array on the Uplink Synchronous Orthogonal Multicarrier DS-CDMA RAKE System in Dispersive Fading Channels

In this paper, the effect of the antenna array (AA) on the performance of the uplink synchronous orthogonal multicarrier DS-CDMA RAKE system is investigated. The bit error rate performance is evaluated under multipath Rayleigh fading channels in terms of the number of antennas, the number of users, and the diversity order. The resultant BER performances are compared to those of the corresponding asynchronous uplink with the A A. The numerical results demonstrate that the additional performance improvement can be obtained by the AA in the synchronous uplink. However, the performance difference between synchronous and asynchronous transmissions decreases as the number of the antennas increases. The capacity of AA- aided orthogonal MC DS-CDMA RAKE systems can be further improved by employing the frequency domain diversity in the synchronous uplink rather than the time domain diversity.

Impact of the antenna shuffling in V-BLAST system using NAK for H-ARQ in correlated fading channels

In this paper, the impact of the antenna shuffling in an antenna-switching scheme using negative acknowledgement for hybrid automatic repeat request (H-ARQ) is investigated and analyzed in the vertical bell labs layered space-time (VBLAST) system, in which the transmit antenna is alternatively switched under retransmission, and the adverse effect of the channel correlation is thus alleviated. Simulation results demonstrate that the average throughput may be further improved by the antenna shuffling in a correlated fading channel without adding much complexity to the process

Joint Optimization of Power Allocation and Detection Ordering for Closed-Loop OSIC System

SUMMARY In this paper, we investigate a detection ordering scheme of OSIC (Ordered Successive Interference Cancellation) systems suitable for power controlled MIMO transmission. Most studies about power controlled systems have mainly focused on strategies for transmitter, while the ordering scheme optimized at open-loop system has not been modified. In a conventional ordering scheme, the ordering process is done according to the largeness and smallness relation of each sub-stream’s SNR. Unlike the conventional scheme, we derive an optimized detection ordering scheme that uses proximity to the optimal SNR. Because of error propagation, our proximity based algorithm is not valid for open-loop MIMO system in many cases. An optimization problem analysis and simulation results show that the system using the proposed ordering scheme outperforms the system using the conventional ordering scheme. Furthermore, due to the nature of QR decomposition, the proposed scheme shows not only lower implementation complexity but also better BER performance compared with the conventional scheme based on pseudo-inverse.

Performance of parallel interference cancellation with reverse-link synchronous transmission technique for DS-CDMA system in multipath fading channels with imperfect power control

This paper analyzes the performance for an improved multistage parallel interference cancellation (PIC) technique with a reverse-link synchronous transmission technique (RLSTT) for DS-CDMA system in a frequency-selective Rayleigh fading channel with an imperfect power control scheme. The performance degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimated as a function of the standard deviation of the PCE. The uncoded bit error performance is evaluated in order to estimate the system capacity. Comparing with the conventional one-stage PIC system, we show achievable gain around 60% by the RLSTT even in the presence of PCE. We conclude that the capacity can be further improved via RLSTT, which alleviates the detrimental effects of the PCE.