Hereinafter, a data re-transmission method is described in brief.
If a transmitting side transmits data, a receiving side receives the data. If data transmission fails, the receiving side requests the transmitting side to re-transmit the corresponding data. An automatic repeat request (ARQ) scheme is generally used as a data re-transmission technique at this time.
The ARQ scheme is to transmit an acknowledgement (ACK) signal and/or a non-acknowledgement (NACK) signal to inform the transmitting side whether data has accurately been received after the receiving side receives the data. If the receiving side transmits the NACK signal to the transmitting side, the transmitting side re-transmits data corresponding to the NACK signal.
The ARQ scheme includes stop-and-wait (SAW) ARQ, go-back-N (GBN) ARQ, and selective-repeat (SR) ARQ.
FIG. 1 is a diagram for explaining a SAW ARQ scheme.
Referring to FIG. 1, ‘A’ and ‘B’ denote a transmitting side and a receiving side, respectively. The horizontal axis represents transmission of a frame with lapse of time. The frame is expressed by ‘fr’.
In the SAW ARQ scheme as illustrated in FIG. 1, a transmitting side waits for an ACK or NACK signal after transmitting data. Upon receipt of the ACK signal, the transmitting side transmits the next data, and upon receipt of the NACK signal, the transmitting side re-transmits the same data. Namely, in the SAW ARQ scheme, only one frame is transmitted at a time. The transmitting side transmits the next data after it is confirmed that data has been successfully transmitted. Although the SAW ARQ scheme may be easily achieved, efficiency is lowered because the next data can not be transmitted until the transmitting side receives the ACK signal after data transmission.
FIG. 2 is a diagram for explaining a GBN ARQ scheme.
In the GBN ARQ scheme, a transmitting side transmits data continuously irrespective of a response message. Referring to FIG. 2, if a data sequence of a third frame is lost while a transmitting side transmits data, the transmitting side re-transmits data from the third frame because it has not received an ACK signal of the third frame. Since the GBN ARQ scheme should assign and manage a sequence number for every frame, its construction may be complicated. Moreover, correctly received data may be discarded.
FIG. 3 is a diagram for explaining an SR ARQ scheme.
The SR ARQ scheme is to re-transmit only data for which NACK signal is received. Referring to FIG. 3, the receiving side which has not received data of a second frame transmits a NACK signal to a transmitting side. The transmitting side then re-transmits data of the second frame representing the NACK signal.
In a data re-transmission method used generally under a high-speed data transmission circumstance, there may a very long time delay. That is, a wireless resource may be wasted in a communication network. Further, errors may frequently occur in data transmitted in a wired or wireless network and much information should be transmitted for a re-transmission request for erroneous data. This may be a cause which can not ensure a data service of high quality.
Meanwhile, a transmitting side (for example, a mobile station) located at a cell boundary or a transmitting side located at a place where it is possible to communicate with two or more receiving sides is influenced by an inferior wireless area. Then the transmitting side is subject to a service of low quality. To overcome this problem, there have been information exchanges between receiving sides (for example, base stations) and complicate signal exchange between the transmitting side and the receiving side. Therefore, resources are wasted and time is delayed in the process of communication between the transmitting side and the receiving side.