1. Field of the Invention
The present invention relates generally to an apparatus and a method for scheduling in a full duplex relay system. More particularly, the present invention relates to scheduling and power control of a relay system, which is capable of stable operation even when sufficient isolation between antennas is not ensured.
2. Description of the Related Art
Coverage holes are caused by regional characteristics such as mountains, trees, and buildings within cells of a mobile communication system.
In order to address these coverage holes, repeaters are installed within the mobile communication system to provide continuous service in these troubled areas within the cells. However, a repeater often degrades the performance in noise amplification.
A relay system, which decodes and forwards a signal from a Base Station (BS), instead of simply amplifying the signal, has been proposed as an improvement over the conventional repeater. This type of improved relay system is being extensively researched to provide the coverage extension and throughput enhancement of a cellular mobile communication system. Specifically, the IEEE 802.16j is standardizing a relay system for practical use, wherein in comparison with a conventional single-hop system, the use of the improved relay system improves performance while reducing deployment and maintenance costs.
Relay schemes may generally be classified into two types: (i) a relay scheme performing only one of transmission or reception using one antenna set, and (ii) a relay scheme simultaneously performing transmission and reception using two antenna sets. The former scheme is referred to as a half duplex relay and the latter scheme is referred to as a full duplex relay.
FIG. 1 is a block diagram of a conventional full duplex relay system, which enables simultaneous communication with an upper node and a lower node using two antenna sets.
Referring to FIG. 1, the full duplex relay system includes a radio transmitter 155, a radio receiver 110, converters 115 and 150 for Analog-to-Digital conversion and Digital-to-Analog conversion, respectively, transmission and reception modems 130 and 120 for modulating and demodulating the signal, a data buffer 125 for temporarily storing data in the data processing, an interference signal controller 135 for controlling interference in the baseband, a delay converter 140 for rejecting interference in the radio band, a size converter 145, and a coupler 160.
The radio transmitter and receiver 155 and 110, the converters 150 and 115, and the transmission and reception modems 130 and 120 may be referred to merely as the transmitter and the receiver, respectively.
When the relay system of FIG. 1 simultaneously transmits and receives over the two antennas by reusing all resources, interference between the antennas is caused. However, this interference relates to the two antennas in the same relay. Therefore the relay system is aware of the transmit signal and can cancel the interference from the signal of the receive antenna. However, for the interference cancellation algorithm, a Signal to inter-antenna Interference Ratio (SIR) basically needs to stay over a certain level. For this reason, the full duplex relay system is installed only in environments where the sufficient isolation between the antennas is ensured.