Abstract:
A hyper throughput packet transmission method for a wireless local area network operating in burst and protection mode is provided. A first CTS frame is sent, comprising an NAV to reserve the medium for a duration. Upon completion of the first CTS frame delivery, a plurality of data frames are delivered to the destination. Upon completion of the data frame delivery, a second CTS frame is sent to reserve the medium for another duration, such that the previous steps form a loop. Delivery of the data frames comprises, a data frame is delivered from the source to the destination, and after the data frame delivered, waiting for an ACK frame from the destination within one SIFS interval. Upon receipt of the ACK frame, if the following data frame is ready, the previous steps loop, otherwise the delivery is complete.

Description:
BACKGROUND  
       [0001]     The invention relates to wireless local area networks, and in particular, to a protection mechanism therefore providing high performance.  
         [0002]     IEEE 802.11 is a wireless local area network standard comprising various purpose protocols. For example, request to send (RTS)/clear to send (CTS) is a medium reservation protocol, and CTS-to-Self is a CTS without a preceding RTS used by 802.11g stations (STAs) to reserve the medium in a basic service set (BSS) requiring “protection”. ERP-OFDM (802.11g) and HS-DSSS (802.11b) are different modulation schemes utilizing the same frequency of 2.4 GHz, therefore “Protection” is required when the BSS is functioning in mixed mode supporting both standards.  
         [0003]      FIG. 1  is a timing chart of conventional RTS/CTS protocol. When RTS/CTS is enabled on a particular station, it will refrain from sending a data frame until the station completes an RTS/CTS handshake with another station, such as an access point (AP). A source SRC initiates the process by sending an RTS frame. A destination DST receives the RTS frame and responds with a CTS frame within a short inter-frame spacing (SIFS) interval. SIFS is a predefined pause subsequently 16 μs in 802.11a (this value is different in 802.11 a/b/g/j). When the SRC receives the CTS frame, the DATA frame is confirmed as delivered. The CTS frame also contains a network allocation vector (NAV) that alerts other stations to refrain from accessing the medium while the SRC transmits the DATA frame. The source SRC and the destination DST, can be an AP/STA pair or STA/AP pair, and the RTS/CTS protocol is applicable for both downlink and uplink transmission. The RTS/CTS handshake provides positive control over the use of the shared medium. The primary reason for implementing RTS/CTS is to minimize collisions among hidden stations.  
         [0004]      FIG. 2   a  shows a wireless network environment comprising both 802.11b and 802.11g stations  204  and  206 , and one AP  202  supporting both standards. The 802.11b standard is an older version supporting only Complementary Code Keying (CCK) modulation. In addition to compatibility with the 802.11b standard, the 802.11g standard also utilizes Orthogonal Frequency Division Multiplexing (OFDM) modulation. Therefore various schemes are proposed to work with the mixed network environment.  
         [0005]      FIG. 2   b  is a timing chart of a conventional CTS-to-self protocol for the wireless network environment in  FIG. 2   a . A source SRC initiates the transmission by sending a CTS frame, and then delivers the DATA 1  frame within one SIFS interval. After delivering the DATA 1  frame, an ACK 1  frame is expected from the destination DST within one SIFS interval. If the ACK 1  frame is not detected in time, the transmission of the DATA 1  frame is deemed a failure. If the ACK 1  frame is received as expected by the SRC, another data transmission is initialized, a DATA 2  frame is delivered after sending a second CTS frame, and a second ACK 2  is expected. The steps recursively loop as long as the DATA frames are available to send, thus the protocol is also referred to as a burst mode. In  FIG. 2   b , the CTS frame contains an NAV for reserving the medium for a period of time. From the falling edge of the CTS frame to the falling edge of the second ACK 2  frame, the NAV protects a total of two DATA frames, two ACK frames, one CTS frame and a plurality of SIFS therebetween. The CTS frame is CCK modulated so all the 802.11b and 802.11g STAs are able to interpret the NAV to keep the medium clear during receipt. Thus, the CCK modulated CTS frames provide mixed mode protection by the NAV therein. In the CTS-to-self mechanism, the source SRC is typically an AP, and the destination DST is a STA. When the BSS does not exceed a predetermined scale, the role of SRC/AP may also be reversed.  
       SUMMARY  
       [0006]     An exemplary embodiment of a hyper throughput mechanism or a packet transmission method for a wireless local area network operating in burst and protection modes is provided. A source transmits data to a destination by the hyper throughput mechanism according to the following steps. A first CTS is sent, comprising an NAV to reserve the medium for a duration. Upon completion of the first CTS delivery, a plurality of data frames are delivered to the destination. Upon completion of data frame delivery, a second CTS is sent to reserve the medium for another duration, such that the steps described form a loop. Delivery of a plurality of data frames comprises the following steps. A data frame is delivered from the source to the destination. After the data frame is delivered, an ACK is received from the destination within one SIFS interval. Upon receipt of the ACK, if the next data frame is ready, the above steps are repeated, until the data frame delivery is complete. The duration the NAV reserves, begins at the falling edge of the first CTS and ends at the falling edge of the second CTS.  
         [0007]     If the ACK is not received within one SIFS interval, the data frame is deemed lost and retransmission is performed. The plurality of data frames may consist of two data frames. The CTS is a CCK modulation packet, and the data frames and the ACK are OFDM modulation packets.  
         [0008]     The source may be an AP supporting 802.11b and 802.11g, and the destination may be a STA supporting 802.11g. Conversely, the source can be a STA and the destination can be an AP.  
         [0009]     Another embodiment provides a hyper throughput method or a packet transmission method for a wireless local area network operating on a hyper throughput protection mode (HTPM). A source transmits data to a destination by the method comprising the following steps. First, an RTS comprising a first NAV is delivered to reserve the medium for a duration. ACTS is expected from the destination within one SIFS interval after the delivery of the RTS. Upon receipt of the CTS, a plurality of data frames are delivered to the destination. The delivery of the data frames consists of the following steps. A data frame is delivered from the source to the destination. An ACK is received from the destination within one SIFS interval after the data frame is delivered. Upon receipt of the ACK, if the next data frame is ready, the previous step is repeated until the data frame delivery is complete. The duration the first NAV reserves, begins at the falling edge of the first RTS and ends at the falling edge of the second ACK received from the destination. The ACK is a CCK modulation packet comprising a second NAV to reserve the medium for a total duration of two ACK, two SIFS and one data frame.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The following detailed description, given by way of example and not intended to limit the invention solely to the embodiments described herein, will best be understood in conjunction with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a timing chart of conventional RTS/CTS protocol;  
         [0012]      FIG. 2   a  shows a wireless network environment comprising both 802.11b and 802.11g stations;  
         [0013]      FIG. 2   b  is a timing chart of a conventional CTS-to-self protocol for the wireless network environment in  FIG. 2   a;    
         [0014]      FIG. 3   a  and  3   b  show an embodiment of the hyper throughput transmission timing chart according to the invention;  
         [0015]      FIG. 4   a  and  4   b  show another embodiment of the hyper throughput transmission timing chart according to the invention; and  
         [0016]      FIG. 5   a  and  5   b  are flowcharts of the hyper throughput mechanism according to  FIG. 3   a  and  3   b ; and  
         [0017]      FIG. 6   a  and  6   b  are flowcharts of the hyper throughput mechanism according to  FIG. 4   a  and  4   b.   
     
    
     DETAILED DESCRIPTION  
       [0018]      FIG. 3   a  shows an embodiment of the hyper throughput transmission timing chart according to the invention. In the mixed local area network shown in  FIG. 2   a , when a source SRC is to deliver data to a destination DST in burst mode, an advanced CTS-to-self mechanism is performed to reduce overhead of the non-DATA frames. First, the SRC initiates the transmission by sending a CTS frame. The CTS comprises an NAV to reserve the medium for a predetermined time. Specifically, the medium is reserved until the next CTS is delivered. In the period between the first and second CTS frames, data transmissions are performed. The data transmission consists of several DATA/ACK pairs. For example,  FIG. 3   a  shows two DATA/ACK pairs in the period between the first and second CTS. The source SRC sends a DATA 1  frame, and waits for an ACK 1  frame from the destination DST within one SIFS interval. If the ACK 1  is not received in time, the transmission of DATA 1  is deemed a failure, and retransmission is performed. If the ACK 1  is correctly received, A DATA 2  frame is then delivered and another ACK 2  frame is expected. The period reserved by the CTS&#39;s NAV maybe adjustable to allow more DATA/ACK delivery. The SIFS interval is essentially between every adjacent frame throughout the transmission, and is part of the conventional standard, thus detailed explanation thereof is omitted herein. In comparison to the conventional CTS-to-self mechanism in  FIG. 2   b , the disclosed CTS provides an NAV capable of protecting more DATA/ACK pairs, thus two or more DATA frames can be transferred more efficiently within one NAV period. In  FIG. 3   a , the destination DST needs no modification, providing full compatibility with present standards.  
         [0019]      FIG. 3   b  shows an improved embodiment of  FIG. 3   a . The source and destination are compromised to handshake in a special mode. A plurality of DATA/ACK pairs are consecutively transferred after the initial CTS frame until all DATA frames are delivered. In this embodiment, the ACK frames is CCK modulated, whereas conventional ACK frames are OFDM modulated. The ACK frames therefore provide NAV to protect successive DATA/ACK transmissions. For example, the NAV of ACK 1  protects DATA 2  and ACK 2 , the NAV of ACK 2  protects DATA 3  and ACK 3 , and so on. In this way, redundant CTS frames are not necessary, and the overhead for burst transmission is reduced. In  FIG. 3   b , the destination DST is modified to operate in the special mode.  
         [0020]     In the embodiment of  FIG. 3   a  and  3   b , the CTS frames are CCK modulated, and the data and ACK frames are OFDM modulated. The source is an AP supporting 802.11b and 802.11g and the destination is a STA supporting 802.11g, therefore the transmission is a downlink. Alternatively, when the BSS is small, the roles of source/destination may be exchanged to implement an uplink.  
         [0021]      FIG. 4   a  shows another embodiment of the hyper throughput transmission timing chart. When transmission is initialized by a RTS/CTS handshake, two pairs of DATA/ACK frames are transferred, and another RTS/CTS handshake takes places thereafter. The RTS frame comprises an NAV protecting the medium until next RTS, thereby the transmission is both in burst mode and protection mode. The RTS, CTS and ACK frames are CCK modulated, whereas the DATA frames are OFDM modulated.  
         [0022]      FIG. 4   b  shows an advanced embodiment of  FIG. 4   a . If the source and destinations compromise a specific mode, the transmission overheads can be further reduced. In this case, the source SRC initiates the transmission by sending an RTS frame. The destination DST returns a CTS frame upon receiving the RTS, such that the RTS/CTS handshake is established. The RTS contains an NAV reserving the medium for a period of time. Thereafter, a plurality of DATA/ACK pairs are transferred within the NAV period. Specifically, the NAV of RTS reserves a period from the falling edge of the RTS to the falling edge of the second ACK 2 , allowing two DATA frames, two ACK frames and all the SIFS intervals therebetween to be transmitted. For example, the NAV of RTS protects CTS, DATA 1 , ACK 1 , DATA 2 , and ACK 2 . The CTS also contains an NAV protecting DATA 1 , ACK 1 , DATA 2 , and ACK 2 .  
         [0023]     In the embodiments of  FIG. 4   a  and  4   b , the ACK frames are CCK modulated, unlike conventional ACK frames utilizing the OFDM modulation. This mechanism, referred to as high throughput protect mode (HTPM), is specifically applied for uplink, thus the source SRC is a STA and the destination DST is an AP. The STA and AP compromise before entering the HTPM. First, the STA and AP authenticate each other by asserting a flag in the association stage, to indicate the support of HTPM. The STA then sends an RTS containing an NAV reserving a duration exceeding one frame, thereby the AP enables HTPM to receive data.  
         [0024]      FIG. 5   a  is a flowchart of the hyper throughput mechanism in  FIG. 3   a . In step  502 , a data frame is provided. In step  504 , the source SRC determines whether the DATA frame is the first frame following the CTS frame. In both cases, step  506  and  508 , the source SRC also determines whether a successive DATA frame is queued for delivery. Yes in step  506  proceeds to step  510 , in which the source SRC sends a CTS protecting two data frames, two ACK frames, one CTS frame and five SIFS intervals. No in step  506  proceeds to step  512 , in which the source SRC sends a CTS protecting one data frame, one ACK frame, and two SIFS intervals. Yes in step  508 , and step  510  both proceed to step  514 . Conversely no in step  508  and step  512  both proceed to step  516 . Instep  514 , the source SRC delivers a DATA frame containing an NAV protecting one DATA frame, two ACK frames, four SIFS intervals and one CTS frame. In step  516 , the source SRC delivers a DATA frame containing an NAV protecting one ACK frame and one SIFS frame. After steps  514  and  516 , in step  530 , the source SRC expects ACK from the destination DST to ensure the delivery is successful. In the event of an error, step  540  performs retransmission or remains idle. Otherwise step  502  is repeated, and another round is initiated.  
         [0025]      FIG. 5   b  is a flowchart of  FIG. 3   b . The redundant CTS is eliminated in the special mode. The transmission is initialized in step  602  with medium competition. In step  604 , the source and destination check support of the HTPM mode. IF not, proceed normal transmission in step  606 , else step  608  is performed. In step  608 , the source SRC and destination DST perform an RTS/CTS handshake, in which the CTS frame contains an NAV protecting one CTS frame, two DATA frames, two ACK frames and four SIFS intervals. Thereafter in step  612 , the source SRC determines whether the following DATA frame exists before sending the present DATA frame. Yes in step  612  proceeds to step  614 , otherwise proceeds to step  616 . In step  614 , the DATA frame is delivered with an NAV protecting one DATA frame, two ACK and three SIFS intervals. In step  616 , the DATA frame is delivered with an NAV protecting one ACK frame and one SIFS interval. Thereafter, in step  618 , the source SRC expects an ACK frame from the destination DST to ensure the delivery is successful. In the event of an error, step  622  provides an exception handler. Otherwise proceed to step  620 , determining whether a next data frame is ready for transmission. Yes in step  620  proceeds to step  612  for another DATA delivery, and no in step  620  returns to step  602 .  
         [0026]      FIG. 6   a  is a flowchart according to  FIG. 4   a . In step  502 , a data frame is provided. In step  504 , the source SRC determines whether the DATA frame is the first frame following the CTS frame. In both cases, step  506  and  508 , the source SRC also determines whether a successive DATA frame is queued for delivery. Yes in step  506  proceeds to step  510 , in which the source SRC sends an RTS frame protecting two data frames, two ACK frames, one CTS frame, one RTS frame and five SIFS intervals. No in step  506  proceeds to step  512 , in which the source SRC sends an RTS frame protecting one data frame, one ACK frame, one CTS frame and three SIFS intervals. Yes in step  508 , and step  510  both proceed to step  514 . Conversely no in step  508  and step  512  both proceed to step  516 . In step  514 , the source SRC delivers a DATA frame containing an NAV protecting one DATA frame, two ACK frames, four SIFS intervals and one RTS frame. In step  516 , the source SRC delivers a DATA frame containing an NAV protecting one ACK frame one RTS frame and two SIFS frame. After steps  514  and  516 , in step  530 , the source SRC expects ACK from the destination DST to ensure the delivery is successful. In the event of an error, in step  540 , an exception handler performs retransmission or remains idle. Otherwise step  502  is repeated, and another round is initiated.  
         [0027]      FIG. 6   b  is a flowchart of the hyper throughput mechanism in  FIG. 4   b . Steps  602 ,  604  and  606  are identical to  FIG. 5   b . Instep  608 , the source SRC and destination DST perform an RTS/CTS handshake, in which the CTS frame contains an NAV protecting one CTS frame, two DATA frames, two ACK frames and five SIFS intervals. Thereafter in step  612 , the source SRC determines whether the following DATA frame exists before sending the present DATA frame. Yes in step  612  proceeds to step  614 , otherwise proceeds to step  616 . In step  614 , the DATA frame is delivered with an NAV protecting one DATA frame, two ACK and three SIFS intervals. In step  616 , the DATA frame is delivered with an NAV protecting one ACK frame and one SIFS interval. Thereafter, in step  618 , the source SRC expects an ACK frame from the destination DST to ensure the delivery is successful. In the event of an error, step  622  provides an exception handler. Otherwise proceed to step  620 , determining whether a next data frame is ready for transmission. Yes in step  620  proceeds to step  612  for another DATA delivery, and no in step  620  returns to step  602 .  
         [0028]     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.