1. Field of the Invention
The present invention relates to a wireless local area network (WLAN) and, more particularly, to a system for performing an immediate retransmission over a WLAN and a method therefor.
2. Description of Related Art
The existing IEEE 802.11 standard for WLAN was published in 1997. In the IEEE 802.11 standard, physical layer (PHY) and medium access control (MAC) operations are defined. Also, rules of wireless medium access are defined in the IEEE 802.11 distributed coordination function (DCF). Wireless networks have now become a particularly common network. DCF is a contention based function and it takes advantages of the carrier sense multiple access/collision avoidance (CSMA/CA) technique for controlling access. DCF takes a positive acknowledgement (ACK) as means for determining whether receiving is correct or not since WLAN is not a reliable transmission medium. As shown in
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An object of the present invention is to provide a system for immediate retransmission over a WLAN and a method therefor so as to decrease the times of timeout occurrence, increase channel reuse ratio, and thus increase network system performance.
One aspect of the present invention is to provide in a WLAN system including a first mobile station, a second mobile station, and an AP or LN wherein the first mobile station intends to transmit data to the second mobile station, a method for an immediate retransmission comprising the steps of in a data transmission stage causing the first mobile station to transmit a data frame to the second mobile station; in a retransmission request stage causing the AP or the LN to broadcast a retransmission.request in response to detecting that the second mobile station fails to receive the data frame; and in an immediate retransmission stage causing the first mobile station to immediately retransmit the data frame in response to receiving the retransmission.request.
Another aspect of the present invention is to provide a system for an immediate retransmission over a WLAN, comprising a first mobile station for transmitting a data frame; a second mobile station for receiving the data frame; and an AP or LN adapted to broadcast a retransmission.request in response to detecting that the second mobile station fails to receive the data frame, wherein the first mobile station is adapted to immediately retransmit the data frame in response to receiving the retransmission.request.
Other objects, advantages, and novel features of the invention will become more apparent from the detailed description when taken in conjunction with the accompanying drawings.
FIGS. 1(a) and 1(b) show processes of a failed data transmission from the transmitting terminal to the receiving terminal and a retransmission thereof over WLAN respectively;
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At this time, AP 21 monitors all transmitted data frames. If AP 21 detects that mobile station 23 successfully receives the data frame and AP 21 also successfully receives the data frame, mobile station 23 will wait a SIFS of time prior to replying with an ACK. To the contrary, if AP 21 detects that there is a frame loss (i.e., a (cyclical redundancy check) CRC error is found by AP 21 after receiving the data frame) and mobile station 23 is unable to successfully receive the data frame, AP 21 broadcasts a retransmission.request to all transmitters (i.e., mobile station 22) since data has been lost and also AP 21 is not aware which mobile station previously transmitted the data frame. Mobile station 22 is informed of the retransmission.request and is thus able to immediately retransmit the lost data frame without contention.
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In view of the above, the invention is able to detect all data frames transmitted from one mobile station to the other mobile station by means of AP or LN by broadcasting. In case of frame loss due to signal interference or collision, AP or LN can detect such loss by finding a CRC error. AP or LN will immediately broadcast a retransmission.request to the transmitter about the frame loss within a SIFS of time. The informed transmitter is thus able to immediately retransmit the lost data frame without waiting a period of time. As such, the invention can eliminate both unnecessary timeout and bandwidth waste. Further, the invention can increase the network system performance by taking advantage of the precious network resource. Furthermore, the invention can increase retransmission speed. In addition, the invention can operate normally even in an environment having high frame loss ratio. Moreover, the invention is fully compatible with the existing IEEE 802.11 standard.
While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.