In this paper, we propose and analyze a multi-level acknowledgement scheme for hybrid ARQ (H-ARQ) systems, which modifies the general ACK/NAK signals to represent multilevel information. For instance, the other signals except the ACK/NAK signals may be used for scheduling of retransmission in the H-ARQ scheme, which results in increasing the resolution of the uplink channel estimation signals. Simulation results demonstrate that when the retransmission interval is set to the optimal length, the proposed H-ARQ scheme shows a 0.5-2 dB gain with properly selected parameters.

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.

This paper presents a Fault-Tolerant Object Group (FTOG) model that provides the group management service and the fault-tolerance service for consistency maintenance and state transparency. Through Intelligent Home Network Simulator, we verify that FTOG model supports both of reliability and the stability of the distributed system.