A general data retransmission method will hereinafter be described in detail.
If a transmission end transmits data, a reception end receives the data from the transmission end. If a failure in data transmission occurs, the reception end requests retransmission of the corresponding data. In this case, an Automatic Repeat reQuest (ARQ) scheme has been widely used as a general data retransmission method.
According to the above-mentioned ARQ scheme, after the reception end has received the data, it transmits an acknowledgement (ACK) signal and/or a non-acknowledgement (NACK) signal, such that the reception end informs the transmission end whether data has been correctly received. If the transmission end receives the NACK signal, it retransmits corresponding data. The above-mentioned ARQ scheme has three kinds of ARQ schemes, i.e., a Stop-And-Wait (SAW) ARQ scheme, a Go-Back-N (GBN) ARQ scheme, and a Selective-Repeat (SR) ARQ scheme.
FIG. 1 is a conceptual diagram illustrating the SAW ARQ scheme.
Referring to FIG. 1, “A” is a transmission end, and “B” is a reception end. A horizontal axis indicates that a frame transmission after the lapse of time. This frame is denoted by “fr”.
As shown in FIG. 1, according to the SAW ARQ scheme, the transmission end transmits data, and waits for the ACK or NACK signal. If the transmission end receives the ACK signal, it transmits the next data. Otherwise, if the transmission end receives the ACK signal, it retransmits the same data. In other words, the SAW ARQ scheme transmits only one frame at one time. After the transmission end recognizes that data has been successfully transmitted to a desired destination, it transmits the next data. The above-mentioned SAW ARQ scheme can be easily implemented. However, the transmission end is unable to transmit the next data until receiving the ACK signal associated with data transmission, resulting in low efficiency.
FIG. 2 is a conceptual diagram illustrating the GBN ARQ scheme.
The GBN ARQ scheme enables the transmission end to continuously transmit data, irrespective of a response message. Referring to FIG. 2, a data sequence of a third frame is lost while the transmission end transmits data. The transmission end has not received the ACK signal from the ACK signal of the third frame, such that it retransmits data from the third frame.
The GBN ARQ scheme must assign a sequence number to each frame, and must manage individual frames, such that its implementation may be unexpectedly complicated. Also, the GBN ARQ scheme may discard all of the correctly-received data.
FIG. 3 is a conceptual diagram illustrating the SR ARQ scheme.
The SR ARQ scheme has been designed to retransmit only specific data which has received the NACK signal. Referring to FIG. 3, the reception end has not received data of a second frame. Therefore, the reception end transmits the NACK signal to the transmission end. The transmission end which has received the NACK signal retransmits data of a frame denoted by the NACK signal to the reception end.
According to a packet-based data transmission scheme, there is needed a higher data rate. According to a high-speed data transmission environment, a new coding rate or a new modulation method is being intensively developed. Therefore, there is proposed a hybrid ARQ (HARQ) scheme suitable for a high-speed data transmission environment.
If data is faulty or erroneous data, the ARQ scheme discards this data. However, according to the HARQ scheme, the reception end stores the erroneous data in a buffer, combines the stored data with the retransmitted data, and applies a forward error correction (FEC) to the combined resultant data. In other words, the HARQ scheme is considered that the FEC scheme is combined with the ARQ scheme. In this case, the HARQ scheme can be classified into four types.
FIG. 4a is a first type of the HARQ scheme.
Referring to FIG. 4a, according to the first type of the HARQ scheme, the reception end attaches an error detection code to data, such that it primarily detects the FEC. In this case, if the packet has the remaining errors, the reception end requests data retransmission from the transmission end. The reception end discards the erroneous packet, the transmission end applies the same FEC code as that of the discarded packet to another packet to be retransmitted, and transmits the resultant packet.
FIG. 4b is a second type of the HARQ scheme.
This second type of the HARQ scheme may also be called an incremental redundancy (IR) ARQ scheme. Referring to FIG. 4b, according to the second type of the HARQ scheme, the reception end does not discard the first transmission packet, and stores it in a buffer. The reception end combines the information stored in the buffer with retransmitted redundancy bits. During the data retransmission time, the transmission end retransmits only parity bits other than data bits. The parity bits retransmitted by the transmission end are changed to others whenever data is retransmitted.
FIG. 4c is a third type of the HARQ scheme.
The third type of the HARQ scheme is a specific case of the second type. Each packet can be self-decodable. If the transmission end retransmits data, it configures the packet including both the erroneous part and the data part, and then retransmits the configured packet. This third type of the HARQ scheme can perform the decoding more correctly than the above-mentioned second type of the HARQ scheme, whereas it has a coding gain less than that of the second type of the HARQ scheme.
FIG. 4d is a fourth type of the HARQ scheme.
Referring to FIG. 4d, according to the fourth type of the HARQ scheme, a specific function is added to the first type of the HARQ scheme. In more detail, this specific function enables the first reception data of the reception end to be stored, and allows this stored data to be combined with retransmission data. This fourth type of the HARQ scheme is called a Metric Combining (MC) scheme or a Chase Combining (CC) scheme. The above-mentioned fourth type of the HARQ scheme is advantageous to a Signal to Interference Noise Ratio (SINR) aspect. The parity bits of retransmission data are always equal to each other.
If data may be lost or there arises erroneous Tx (transmission) data, the above-mentioned data retransmission methods can recover original data.
However, according to conventional arts, a delay of a data transfer time for each retransmission method may unexpectedly increase, such that resources of a communication network may be unnecessarily consumed. During the data transmission time, unexpected errors may frequently occur in wired or wireless data. In order to request retransmission of faulty or erroneous data, the above-mentioned conventional arts must transmit a large amount of information for the retransmission request to a destination. As a result, the reception end may not guarantee a desired-level service.