The development of communication technology makes possible to provide various signals such as video, audio and data to users through a satellite although the users are moving around. In order to eliminate a shadow area in a satellite communication network, repeaters are installed at the ground.
The satellite digital multimedia broadcasting (DMB) in Republic of Korea and the satellite-digital multimedia broadcasting (S-DMB) in Europe are representative satellite communication system including repeaters. A repeater is defined as gap-filler in the satellite DMB of Republic of Korea, and a repeater is defined as an intermediate module repeater in the S-DMB of Europe. In a satellite communication network, a repeater is classified as a simple amplifying repeater and as a frequency transforming repeater. The simple amplifying repeater receives a signal from a satellite, amplifies the received signal in the same band, and relays the amplified signal to a terminal. The frequency transforming repeater transforms the frequency of the signals received from the satellite, and relays the transformed signals to a terminal.
In the terminal of the satellite communication network, multipath fading occurs to receive more than two signals. In order to stably receive the multi path fading signals, the terminal includes a CDMA rake receiver.
In the satellite communication network, a satellite simply radiates signals to the ground. A repeater simply amplifies a signal and relays the amplified signal, or transforms a signal to a signal with other frequency band and relays the transformed signal. Therefore, a terminal cannot obtain diversity gain through signals received from the satellite and from the repeaters.
For example, if a space time block code (STBC) defined in 3GPP WCDMA based IMT-2000 wireless interface specification is used, multipath fading can be reduced without requiring additional bandwidth in a multi antenna system, thereby obtaining diversity gain.
However, the STBC scheme cannot be applied to the conventional signal transmission scheme used in the satellite and the repeaters in the satellite communication network. That is, in order to apply the STBC scheme, a transmitting end is required to have two transmitting antennas and transmits time space block codes through the two transmitting antennas, and a terminal must be capable of obtaining time and space correlation of signals received from different antennas. Therefore, it is impossible to apply the STBC scheme into the conventional signal transmission scheme used in the satellite communication network.
Therefore, there is demand for a method to apply the space time block code (STBC) scheme into a satellite communication system without a gapfiller. Especially, there is demand for a method for obtaining diversity gain at a terminal by transmitting signal with STBC applied through reading a satellite and a repeater as two transmitting antennas, and a method for making a terminal to receive signals from a satellite and a repeater like receiving two signals from one transmitting end.
Furthermore, there is demand for a method for detecting a corresponding signal at a terminal by decoding a STBC coded signal received from a satellite and a repeater, and a method for improving efficiency of receiving a signal by performing channel estimation, channel compensation and channel prediction at a terminal.