Duho Rhee

Adaptive modulation and coding on multipath Rayleigh fading channels based on channel prediction

Due to the time variant characteristic of wireless communication channels, channel-state-information (CSI) becomes out-of-date if we consider the CSI feedback delay. Thus, channel prediction is required to mitigate this phenomenon. In this paper, we propose an adaptive modulation and coding (AMC) scheme using channel prediction on multipath Rayleigh fading channels and evaluate the performance of the proposed scheme. For a given modulation and coding set (MCS), the average packet error rates are derived as functions of the predicted channel information and the prediction error variance. Based on CSIs, the required transmit power is obtained for each MCS option, simulation results show that the performance degradation due to feedback delay can be compensated by the proposed scheme

Adaptive Modulation Technique with Partial CQI for Multiuser OFDMA Systems

In this paper, we present a new scheme for sub-band allocation in multiuser downlink orthogonal frequency division multiple access (OFDMA) systems with partial channel quality information (CQI). Our objective is to maximize the total throughput of the system under the constraints of transmit power. In previous methods, each user in a cell transmits CQI of its all sub-bands to the base station, which requires extremely high feedback overhead. Thus, we propose an efficient sub-band allocation algorithm in which each user transmits partial CQI and one additional information to reduce the amount of feedback. Simulation results show that we can greatly reduce the amount of feedback than full feedback system

Iterative narrowband jamming rejection technique for coded OFDMA-CDM systems

The robustness to jamming signal is an important property for military communication systems. Some previous work has shown that the frequency domain code division multiplexing (CDM) efficiently rejects the interference. In general, however, the jamming signal has higher power than ordinary interference which leads to insufficient jamming rejection performance of these schemes. To mitigate this insufficiency, we propose optimal receiver structures in mean sqaure error (MSE) sense in the presence of narrowband jamming signal. Also these receivers are extended to iterative regime. By this approach, high power narrowband jamming signal could be efficiently rejected. The robustness to jamming signal is an important property for military communication systems. Some previous work has shown that the frequency domain code division multiplexing (CDM) efficiently rejects the interference. In general, however, the jamming signal has higher power than ordinary interference which leads to insufficient jamming rejection performance of these schemes. To mitigate this insufficiency, we propose optimal receiver structures in mean sqaure error (MSE) sense in the presence of narrowband jamming signal. Also these receivers are extended to iterative regime. By this approach, high power narrowband jamming signal could be efficiently rejected.

Performance analysis of a decode-and-forward based hybrid-ARQ protocol

Cooperative hybrid-ARQ protocols have been widely studied because the efficiency of time resources of them is higher than that of cooperative protocols. In this paper, a cooperative hybrid-ARQ protocol based on incremental redundancy hybrid-ARQ technique is proposed and analyzed with respect to the relay location. Based on the analysis, the optimum initial rate is searched and the maximum throughput is obtained with respect to the relay location.

Multiuser adaptive transmission technique for time-varying frequency-selective fading channels

This paper proposes an efficient multiuser adaptive modulation and coding (AMC) scheme that considers inevitable feedback delay by employing short-term and long-term channel state information (CSI) in time-varying frequency-selective fading channels. By taking the statistic of the true signal-to-noise ratio (SNR) at a given predicted SNR value into account, the required transmit power to meet the target packet-error-rate (PER) can be obtained and used for user selection, power allocation, and modulation and coding set (MCS) selection. In addition, a simple and useful approximation method of obtaining the required transmit power is proposed. The performance of the proposed scheme is shown to be much better than that of conventional schemes without considering the feedback delay or the prediction error. The proposed scheme can also reduce the feedback resource while maintaining the system throughput by allocating different feedback resources to different users according to their prediction error variances.

A Pragmatic Adaptive Transmission Scheme with Low-Rate Feedback Using Two-Step Partial CQI for Multiuser OFDMA Systems

In this paper, we investigate an efficient user selection and sub-band allocation algorithm in which each user transmits two-step partial CQI to reduce the amount of feedback in multi-user downlink OFDMA systems. Simulation results show that we can greatly reduce the feedback rate at the expense of negligible performance degradation compared to the full CQI feedback schemes or that we can greatly improve the performance with slightly reduced feedback rate compared to conventional partial CQI feedback schemes.

Opportunistic Scheduling with Partial CQRI Feedback in OFSDMA Systems

In this paper, we propose a novel and efficient OS scheme with partial CQRI feedback. The average system capacity of the proposed OS scheme with partial CQRI feedback is analyzed as well as those of the conventional OS schemes with full and partial CQI feedbacks. Analysis and simulation results show that the proposed scheme improves system performance in terms of the average system capacity, especially when the amount of feedback per user is restricted to be small. It is shown that when the number of users is 100, the proposed scheme achieves 90% capacity of the full CQI feedback scheme, requiring only 4% and 60% feedback rate of the conventional full and partial CQI feedback schemes, respectively.

Efficient Adaptive Transmission Technique for Coded Multiuser OFDMA Systems

In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OFDMA systems with practical codeword lengths is investigated. Also, in order to keep the feedback overhead within a practical range, a two-step partial CQI scheme is adopted, which has both better performance and reduced feedback overhead compared to conventional partial CQI schemes. By allowing a long codeword block across all allocated sub-bands with appropriate power and modulation order allocation rather than using short codeword blocks to each sub-band, high coding gain can be obtained, which leads to performance improvement.