6.Retransmission Control

Retransmission control under ARQ uses three basic systems. The SAW system sends a transmission frame, pauses to confirm that no retransmission request is received within a certain time interval, and then sends the next frame. The SR system continuously sends transmission frames until receiving a retransmission request from the reception side, at which time it retransmits only the requested frame. While this system offers the highest transmission efficiency, hardware, technology and control are complex and may lead to buffer overflow in some cases. The GBN system continuously sends transmission frames until receiving a retransmission request from the reception side, at which time it retransmits the requested frame and all subsequent frames.

By selectively adopting the relative advantages of these basic systems, NTT DOCOMO has developed a new technology called WORM-ARQ that can maintain stability at high efficiency by appropriately switching between the SR and GBN systems in accordance with the required depending on transmission quality.

Example WORM-ARQ Operation

Created 1999/03