1. Field of the Invention
The present invention relates to the technical field of medium access control (MAC) layer in wireless networks and, more particularly, to an enhanced direct link transmission method and system for wireless local area networks.
2. Description of Related Art
Currently, IEEE 802.11 Standard is the most popular MAC protocol for wireless local area networks (WLANs). Based on the specifications of IEEE 802.11, data frame transmission between any two mobile stations (e.g., cellular phones, PDAs, notebooks, or other devices with wireless communication capability) under an infrastructure WLAN is performed via access point (AP) as shown in
In the basic method, it is assumed that mobile station X desires to transmit data to AP. Prior to transmitting a data frame, mobile station X must sense other transmission. Typically, it is necessary to wait a period of time consisting of DCF inter frame space (DIFS) period and a random number of backoff time slots. Mobile station X will transmit data frame to AP if there is no data frame transmission at the end of the above waiting time (DCF+backoff slots). After receiving the data frame, AP will wait short inter frame space (SIFS) time prior to transmitting an acknowledgement (ACK) to mobile station X.
In the RTS/CTS method, it is assumed that mobile station X desires to transmit data to AP. Prior to transmitting a data frame, mobile station X must detect whether any other mobile station is transmitting data frame. Typically, it is necessary to wait a period of time consisting of DIFS time and a randomly selected backoff slot time. Mobile station X will transmit a request to send (RTS) to AP if there is no data frame transmission at the end of the above waiting time (DCF+backoff slots). After receiving the RTS, AP will wait SIFS time prior to transmitting a clear to send (CTS) to mobile station X. After receiving the CTS, mobile station X will transmit data frame to AP after the SIFS time has elapsed. After receiving the data frame, AP will transmit ACK to mobile station X. The RTS/CTS method is designed to solve the hidden terminal problem.
As shown in
In IEEE 802.11e draft (IEEE 802.11e/D6.0, Draft Supplement to Part II: Wireless medium access control (MAC) and physical layer (PHY) specifications: MAC enhancements for quality of service (QoS), IEEE, November 2003), a modification to the original 802.11 is proposed in which a mobile station is allowed to directly transmit data frame to any other mobile station by AP if the AP exists in the WLAN as shown in
In view of the DLP method employed by the above 802.11 specifications and 802.11e draft, it is found that AP is required in their operations. As such, the times of exchanging control frames increase, resulting in a decrease of throughput of the WLAN. Moreover, if AP is out of order, mobile stations X and Y cannot exchange data frame even though they are adjacent to each other (i.e., they can receive signals from each other). Thus, it is desirable to lower the possibility of AP intervention as experienced in prior 802.11 specifications and 802.11e draft, decrease the time of exchanging data frame, carry out a direct link between two mobile stations, and comply with existing IEEE 802.11 specifications.
The object of the present invention is to provide an enhanced direct link transmission method and system for wireless local area networks, so as to lower the possibility of AP intervention, decrease the time of exchanging data frame, and carry out a direct link between two mobile stations.
One aspect of the present invention is to provide an enhanced direct link transmission method for wireless local area networks. The wireless local area network comprises an access point (AP), a first mobile station and a second mobile station. The first mobile station is adapted to directly transmit data to the second mobile station. When the first mobile station is adjacent to the second mobile station, the method comprises the steps of: (A) causing the first mobile station to transmit an EDLP.request; (B) responsive to receiving the EDLP.request, the second mobile station replying an EDLP.response containing a result code indicating SUCCESS to the first mobile station in a first period of time; and (C) responsive to receiving the EDLP.response, the first mobile station transmitting a data frame to the second mobile station.
Another aspect of the present invention is to provide an enhanced direct link transmission method for wireless local area networks. The wireless local area network comprises an access point (AP), a first mobile station and a second mobile station. The first mobile station is adapted to directly transmit data to the second mobile station. When the first mobile station is adjacent to the second mobile station, the method comprises the steps of: (A) causing the first mobile station to transmit an EDLP.request; (B) causing the AP to reply an EDLP.response containing a result code indicating NOT_ADJACENT to the first mobile station in a second period of time if the second period of time is longer than the first period of time; and (C) responsive to receiving the EDLP.response, the first mobile station transmitting a data frame to the AP.
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.
a depicts an EDLP operation between adjacent mobile stations X and Y according to the invention;
b depicts the EDLP operation between non-adjacent mobile stations X and Y according to the invention;
a,
5
b, and 5c depict operations of transmitting data from mobile station X to mobile station Y as proposed by IEEE 802.11, DLP in IEEE 802.11e draft, and the EDLP according to the invention respectively; and
The system and method of the invention are embodied in IEEE 802.11 WLAN in which an enhanced direct link protocol (EDLP) is employed for facilitating data transfer between two mobile stations. Following is a detailed description of the EDLP operation. In
In
The EDLP.request contains information such as MAC address of mobile stations X and Y, ID (e.g., association ID (AID), MAC address, or any other codes for identifying purpose) of AP, supported rates, security, etc. The EDLP.response contains information such as result code or status code, MAC address of mobile stations X and Y, ID (e.g., AID, MAC address, or any other codes for identifying purpose) of AP, supported rates, security, etc. Thus, mobile station X or AP can respond based on the result code in the EDLP.response.
In
With reference to FIGS. 5(a), 5(b), and 5(c), operations of transmitting data from mobile station X to mobile station Y as proposed by IEEE 802.11, DLP in IEEE 802.11e draft, and EDLP according to the invention are respectively shown. Note that time interval between data frames is omitted. It is seen that two times of DCF contention and eight times of data transmission are performed by IEEE 802.11, one time of DCF contention and six times of data transmission are performed by DLP in IEEE 802.11e draft, and one time of DCF contention and four times of data transmission are performed by EDLP of the invention. Therefore, EDLP of the invention can achieve direct data transfer by a minimum number of data frames. As a result, advantages such as less time for data transmission and less chance of contention and collision can be obtained.
With reference to
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.
Number | Date | Country | Kind |
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093135971 | Nov 2004 | TW | national |