Abstract:
A system comprises a monitoring module operative to monitor traffic on a wireless medium, the traffic belonging to one or more of two different access classes (ACs), one access class (AC) being a higher-priority AC and the other being a lower-priority AC; a throughput adaptation module communicatively coupled to the monitoring module and operative to dynamically generate data corresponding to one or more AC-sensitive parameters based on the monitored traffic and on a desired throughput ratio between the two different ACs; and a wireless communication module communicatively coupled to the throughput adaptation module and operative to communicate the data to one or more wireless stations on the wireless medium.

Description:
COPYRIGHT NOTICE 
       [0001]    A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       TECHNICAL FIELD 
       [0002]    This invention relates generally to wireless local area networks, and more particularly provides a system and method for controlling throughput of access classes (ACs) in a wireless local area network (WLAN). 
       BACKGROUND 
       [0003]    As users experience the convenience of wireless connectivity, they arc demanding increasing support. Typical applications over wireless networks include video streaming, video conferencing, distance learning, etc. Because wireless bandwidth availability is restricted, quality of service (QoS) management is increasingly important in 802.11 networks. 
         [0004]    The original 802.11 media access control (MAC) protocol was designed with two modes of communication for wireless stations (STAs). The “first mode, Distributed Coordination Function (DCF), is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), sometimes referred to as “listen before talk.” A wireless station (STA) waits for a quiet period on the network and then begins to transmit data and detect collisions. The second mode, Point Coordination Function (PCF), supports time-sensitive traffic flows. Using PCF, wireless access points (APs) periodically send beacon frames to communicate network identification and management parameters specific to the wireless local area network (WLAN). Between beacon frames, PCF splits time into a contention period (CP) where the STAs implement a DCF protocol, and a contention-free period (CFP) where an AP coordinates access by the various STAs based on QoS requirements. 
         [0005]    Because DCF and PCF do not differentiate between traffic types or sources, IEEE proposed enhancements to both coordination modes to facilitate QoS. These changes are intended to fulfill critical service requirements while maintaining backward-compatibility with current 802.11 standards. 
         [0006]    Enhanced Distributed Channel Access (EDCA) introduces the concept of traffic categories (or access classes). Using EDCA, STAs try to send data after detecting that the wireless medium is idle for a set time period defined by the corresponding access class (AC). A higher-priority AC will have a shorter wait time than a lower-priority AC. While no guarantees of service are provided, EDCA establishes a probabilistic priority mechanism to allocate bandwidth based on ACs. 
         [0007]    The IEEE 802.11e EDCA standard provides QoS differentiation by grouping traffic Into four ACs, i.e., voice, video, best effort and background. Each transmission frame from the upper layers bears a priority value (0-7), which is passed down to the MAC layer. Based on the priority value, the transmission frames are mapped into the four ACs at the MAC layer. The voice (VO) AC has the highest priority; the video (VI) AC has the second highest priority; the best effort (BE) AC has the third highest priority; and the background (BK) AC has the lowest priority. Each AC has its own transmission queue and its own set of AC-sensitive medium access parameters. Traffic prioritization uses the medium access parameters—the arbitration interframe space (AIFS) interval, contention window (CW, CWmin and CWmax), and transmission opportunity (TXOP)—to ensure mat a higher priority AC has relatively more medium access opportunity than a lower priority AC. 
         [0008]    Generally, in BDCA, AIFS is the time interval that a STA must sense the wireless medium to be idle before invoking a backoff mechanism or transmission. A higher priority AC uses a smaller AIFS interval The contention window (CW, CWmin and CWmax) indicates the number of backoff time slots until the STA can attempt another transmission. The contention window is selected as a random backoff number of slots between 0 and CW. CW starts at CWmin. CW is essentially doubled every time a transmission fails until CW reaches its maximum Value CWmax. Then, CW maintains this maximum value CWmax until the transmission exceeds a retry limit. A higher priority AC uses smaller CWmin and CWmax. A lower priority AC uses larger CWmin and CWmax. The TXOP indicates the maximum duration that an AC can be allowed to transmit frames after acquiring access to the medium. To save contention overhead, multiple transmission frames can be transmitted within one TXOP without additional contention, as long as the total transmission time does not exceed the TXOP duration. 
         [0009]    To reduce, the probability of two STAs colliding, because the two STAs cannot hear each other, the standard defines a virtual carrier sense mechanism. Before a STA initiates a transaction, the STA first transmits a short control frame called RTS (Request To Send), which includes the source address, the destination address and the duration of the upcoming transaction (i.e. the data frame and the respective ACK), Then, the destination STA responds (if the medium is free) with a responsive control frame called CTS (Clear to Send), which includes the same duration information. All STAs receiving either the RTS and/or the CTS set a virtual carrier sense indicator, i.e., the network allocation vector (NAV), for the given duration, and use the NAV together with the physical carrier sense when sensing the medium as idle or busy. This mechanism reduces the probability of a collision in the receiver area by a STA that is “hidden” from the transmitter STA to the short duration of the RTS transmission, because the STA hears the CTS and “reserves” the medium as busy until die end of the transaction. The duration information in the RTS also protects the transmitter area from collisions during the ACK from STAs that are out of range of the acknowledging STA, Due to the fact that the RTS and CTS are short, the mechanism reduces the overhead of collisions, since these transmission frames are recognized more quickly than if the whole data transmission frame was to be transmitted (assuming the data frame is bigger than RTS). The standard allows for short data transmission frames, i.e., those shorter than an RTS Threshold, to be transmitted without the RTS/CTS transaction. 
         [0010]    With these medium access parameters, EDCA works in the following mariner: 
         [0011]    Before a transmitting STA can initiate any transmission, the transmitting STA must first sense the channel idle (physically and virtually) for at least an AIFS time interval. If the channel is idle after the initial AIFS interval, then the transmitting STA initiates an RTS transmission and awaits a CTS transmission from the receiving STA. 
         [0012]    If a collision occurs during the RTS transmission or if CTS is not received, then the transmitting STA invokes a backoff procedure using a backoff counter to count down a random number of backoff time slots selected between 0 and CW (initially set to CWmin). The transmitting STA decrements the backoff counter by one as long as the channel is sensed to be idle. If the transmitting STA senses the channel to be busy at any time during the backoff procedure, the transmitting STA suspends its current backoff procedure and freezes its backoff counter until the channel is sensed to be idle for an AIFS interval again. Then, if the channel is still idle, the transmitting STA resumes decrementing its remaining backoff counter. 
         [0013]    Once the backoff counter reaches zero, the transmitting STA initiates an RTS transmission and awaits a CTS transmission from the receiving STA. If a collision occurs during the RTS transmission or CTS is not received, then the transmitting STA invokes another backoff procedure, possibly increasing the size of CW. That is, as stated above, after each unsuccessful transmission, CW is essentially doubled until it reaches CWmax. After a successful transmission, CW returns to its default value of CWmin. During the transaction, the STA can initiate multiple frame transmissions without additional contention as long as the total transmission time does not exceed the TXOP duration. 
         [0014]    The level of QoS control for each AC is determined by the combination of the medium access parameters and the number of competing STAs in the network. The default EDCA parameter values used by non-AP QoS stations (QSTAs) are identified in the table of  FIG. 1 . A TXOP_Limit value of 0 indicates that a single MAC service data unit (MSDU) or MAC protocol data unit (MPDU), in addition to a possible RTS/CTS exchange or CTS to itself, may be transmitted at any rate for each TXOP. 
         [0015]    The Hybrid Coordination Function (HCF) is another 802.11e wireless protocol Generally, HCF uses the concepts of PCF, but substitutes the protocols of DCF during the contention period (CP) with the improved protocols of EDCA. Using HCF, a hybrid coordinator (HC), typically co-located with the AP, periodically sends beacon frames. Each beacon frame includes a beacon interval a timestamp, a service set identifier (SSID) identifying the specific wireless LAN, supported rates, parameter sets identifying implemented signaling protocols (frequency hopping spread spectrum, direct sequence spread spectrum, etc.), capability information identifying communication requirements (WEP, etc.), a traffic indication map (TIM) identifying data frames waiting in the AP&#39;s buffer, and a contention-free period (CFP) duration. The AP and STAs use the information in the beacon frames to implement HCF. 
         [0016]    Between beacon frames, HCF splits time into a contention-free period (CFP) and a contention period (CP). During the CFP, the AP uses HCF controlled channel access (HCCA) protocols to coordinate access by the various STAs based on QoS requirements. The contention-free period (CFP) typically begins with the receipt of a beacon frame, and ends either upon expiration of the CFP duration, as specified in the beacon frame or upon receiving a CFP-End frame from the HC. During the CP, the AP and STAs use a combination of EDCA and HCCA protocols. Each STA accesses the wireless medium when the wireless medium is determined to be available under EDCA rules or when the STA receives a QoS CF-Poll frame from the HC. In other words, unlike PCF, HCF enables contention-free bursts called controlled access periods (CAPs) during the CP to allow priority traffic to access the wireless medium without contention. At all other times during the CP, the STAs access the wireless medium using EDCA,  FIG. 1B  is a timing diagram illustrating prior art CAP/CP/CFP intervals. As shown, a CFP Repetition interval includes both the CFP and CP. 
         [0017]    Although IEEE 802.11e provides the means to achieve traffic-type differentiation, it does not specify a mechanism enabling throughput control across different ACs. Systems and method are needed to obtain throughput control across different ACs. 
         [0018]    Example prior art references include the following:
   1. U.S. Patent Application Publication No.: US 2005/0271019 A1 Publication Date: Dec. 8, 2005 application Ser No. 10/861,258 Filing Date: Jun. 8, 2005 Title: ACCESS CONTROL AND PROTOCOL FOR PACKET SWITCHED WIRELESS COMMUNICATIONS NETWORKS   2. U.S. Patent Application Publication No.: US 2008/0045050 A1 Publication Date: Mar. 2, 2008 application Ser No. 10/986,244 Filing Date: Nov. 10, 2004 Title: METHOD AND SYSTEM FOR A QUALITY OF SERVICE MECHANISM FOR A WIRELESS NETWORK   3. U.S. Patent Application Publication No.; US 2008/0187840 A1 Publication Date: Aug. 24, 2006 application Ser. No. 11/263,291 Filing Date: Oct. 31, 2005 Title: METHOD AND APPARATUS FOR CONTROLLING WIRELESS MEDIUM CONGESTION BY ADJUSTING CONTENTION WINDOW SIZE AND DISASSOCIATING SELECTED MOBILE STATIONS   4. U.S. Patent Application Publication No.: US 2006/0188301 A1 Publication Date: Sep. 7, 2006 application Ser. No. 11/074,359 Filing Date: Mar. 7, 2005 Title: PACKET-LEVEL SERVICE DIFFERENTIATION FOR QUALITY OF SERVICE PROVISIONING OVER WIRELESS LOCAL AREA NETWORKS   5. U.S. Patent Application Publication No.; US 2006/0291402 A1 Publication Date: Dec. 28, 2008 application Ser. No. 11/417,197 Filing Date; May 4, 2006 Title: APPARATUS AND METHOD FOR PROVIDING ENHANCED WIRELESS COMMUNICATIONS   6. PCT International Publication No.: WO 2008/130021 A2 Publication Date: Dec. 7, 2006 International Application No.: PCT/NO2006/000208 International Filing Date: Jun. 2, 2005 Title: METHOD AND DEVICE FOR ADMINISTRATION OF TRAFFIC IN COMMUNICATION SYSTEM USING A CONTENTION BASED ACCESS CONTROL   
 
       SUMMARY 
       [0025]    In accordance with, a first embodiment, the present invention provides a system comprising a monitoring module operative to monitor traffic on a wireless medium, the traffic belonging to one or more of two different access classes (ACs), one access class (AC) being a higher-priority AC and the other being a lower-priority AC; a throughput adaptation module communicatively coupled to the monitoring module and operative to dynamically generate data corresponding to one or more AC-sensitive parameters based on the monitored traffic and on a desired throughput ratio between the two different ACs; and a wireless communication module communicatively coupled to the throughput adaptation module and operative to communicate the data to one or more wireless stations on the wireless medium. 
         [0026]    The monitoring module may determine dynamically the throughput requirements of the higher-priority traffic on the wireless medium. The monitoring module may determine dynamically the desired throughput ratio between the higher priority AC and the lower-priority AC. The two different traffic classes may include one for voice or video, and one for best effort or background. The system may be operative on the access point. The one or more AC-sensitive parameters may include at least one of AIFSN, TXOP and CWmin for at least one AC. The one or more AC-sensitive parameters may include AIFSN, which is computed based on the following equations; 
         [0000]    
       
         
           
             
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         [0000]    where N 1  refers to the number of higher-priority AC streams, N 2  refers to the number of lower-priority AC streams, 1:ki refers to the desired throughput ratio between the higher-priority AC and the lower-priority AC, τ refers to the steady state probability of channel access for the higher priority STAs, A refers to one of two AIFSN[LP] values, p refers to a probability of selecting value A as the AIFSN[LP] value, f refers to the fractional component of T 1 , D refers to the smallest integer greater than or equal to T 1 , and AIFSN_Lag refers to the difference between AIFSN[LP] and AIFSN[HP]. The one or more AC-sensitive parameters may include TXOP, which is computed based on the equation TXOP[LP]=TXOP[HP]×k, where 1:k refers to the desired throughput ratio between the higher-priority AC and the lower-priority AC. The one or more AC-sensitive parameters may include CWmin, which is computed based on the equation CWmin[LP]=CWmin[HP]/k, where 1:k refers to the desired throughput ratio between higher-priority AC and the lower-priority AC. 
         [0027]    In accordance with another embodiment, the present invention may provide a method comprising monitoring traffic on a wireless medium, the traffic belonging to one or more of two different access classes (ACs), one access class (AC) being a higher-priority AC and the other being a lower-priority AC; dynamically generating data corresponding to one or more AC-sensitive parameters based on the monitored traffic and on a desired throughput ratio between the two different ACs; and communicating the data to one or more wireless stations on the wireless medium. 
         [0028]    The method may further comprise determining dynamically the throughput requirements of the higher-priority traffic on the wireless medium. The method may further comprise determining dynamically the desired throughput ratio between the higher priority AC and the lower-priority AC. The two different traffic classes may include one for voice or video, and one for best effort or background. The method may fee operative on the access point. The one or more AC-sensitive parameters include at least one of AIFSN, TXOP and CWmin for at least one AC. The one or more AC-sensitive parameters may include AIFSN, and the method may further comprise computing the following equations: 
         [0000]    
       
         
           
             
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         [0000]    where N 1  refers to the number of higher-priority AC streams, N 2  refers to the number of lower-priority AC streams, 1:ki refers to the desired throughput ratio between the higher-priority AC and the lower-priority AC, τ refers to the steady state probability of channel access for higher priority STAs, A refers to one of two AIFSN[LP] values, p refers to a probability of selecting value A as the AIFSN[LP] value, f refers to the fractional component of T 1 , D refers the smallest integer greater than or equal to T 1 , and AIFSN_Lag refers to the difference between AIFSN[LP] and AIFSN[HP]. The one or more AC-sensitive parameters may include TXOP, and the method may further comprise computing TXOP[LP]=TXOP[HP]×k, where 1:k refers to tire desired throughput ratio between the higher-priority AC and the lower-priority AC. The one or more AC-sensitive parameters may include CWmin, and the method may further comprise computing CWmin[LP]=CWmin[HP]/k, where 1:k refers to the desired throughput ratio between higher-priority AC and the lower-priority AC. 
         [0029]    In accordance with yet another embodiment, the present invention may provide a system comprising means for monitoring traffic on a wireless medium, the traffic belonging to one or more of two different access classes (ACs), one access class (AC) being a higher-priority AC and the other being a lower-priority AC; means for dynamically generating data corresponding to one or more AC-sensitive parameters based on the monitored traffic and on a desired throughput ratio between the two different ACs; and means for communicating the data to one or more wireless stations on the wireless medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1A  is a table of a prior art EDCA access class (AC) parameter set for 802.11g. 
           [0031]      FIG. 1B  is a timing diagram illustrating prior art CP/CFP intervals. 
           [0032]      FIG. 2A  is a block diagram illustrating a wireless local area network (WLAN) using throughput tuning, in accordance with an embodiment of the present invention. 
           [0033]      FIG. 2B  is a block diagram illustrating details of a WLAN with traffic categories listed, in accordance with an embodiment of the present invention. 
           [0034]      FIG. 3  is a block diagram illustrating details of an AP of  FIG. 2A , in accordance, with an embodiment of the present invention. 
           [0035]      FIG. 4A . is a block diagram illustrating details of an AP MAC controller of  FIG. 3 , in accordance with an embodiment of the present invention. 
           [0036]      FIG. 4B  is a timing diagram illustrating AIFSN differentiation in EDCA. 
           [0037]      FIG. 5  is a block diagram illustrating details of a STA of  FIG. 2A , in accordance with an embodiment of the present invention. 
           [0038]      FIG. 6  is a block diagram Illustrating details of a STA MAC controller of  FIG. 5 , in accordance with an embodiment of the present invention. 
           [0039]      FIG. 7  is a flowchart illustrating a method of tuning throughput across traffic classes, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    The following description is provided to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the embodiments are possible to those skilled in the art, and the generic principles defined herein may be applied to these and other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent, with the principles, features and teachings disclosed herein. 
         [0041]    In one embodiment, the access point (AP) implements an algorithm to tune the EDCA parameters across different ACs to achieve desired throughput ratios. More specifically, the AP monitors the throughput requirements of high priority traffic and then tunes the EDCA parameters across different ACs relative to the high priority traffic to optimize available bandwidth and achieve desired throughput ratios. 
         [0042]      FIG. 2A  is a block diagram illustrating a wireless local area network (WLAN)  200  using throughput tuning in accordance with an embodiment of the present invention. The WLAN  200  includes an AP  205  coupled to a computer network  210 , such as the wide area network (WAN) commonly referred to as the Internet. In one embodiment, the AP  205  is coupled to the computer network  210  via a wired connection, although a wireless connection is also possible. The WLAN  200  also includes three (3) STAs, namely, STA  215   a , STA  215   b  and STA  215   c  (although any number of STAs is possible). Each STA  215   a ,  215   b ,  215   c  is in wireless communication with the AP  205  via the wireless medium. Each STA  215   a ,  215   b ,  215   c  is generally referred to herein as a STA  215 , although each STA  215   a ,  215   b ,  215   c  need not be identical. 
         [0043]    The AP  205  includes an AP medium access control (MAC) controller  220 , which Includes hardware, software and/or firmware operative to control wireless access to the wireless medium by the AP  205  and to control throughput tuning. Details of the AP  205  are provided with reference to  FIG. 3 . Details of the AP MAC controller  220  are provided with reference to  FIG. 4A . 
         [0044]    The STA  215   a  includes a STA MAC controller  225   a ; the STA  215   b  includes a STA MAC controller  225   b ; and the STA  215   c  includes a STA MAC controller  225   c . Each STA MAC controller  225   a ,  225   b ,  225   c  is generally referred to herein as a STA MAC controller  225 , although each STA MAC controller  225   a ,  225   b ,  225   c  need not be identical. Each STA MAC controller  225  includes hardware, software and/or firmware to control wireless access to the wireless medium by each STAs  215 . 
         [0045]    In one embodiment, the AP MAC controller  220  effects throughput tuning by monitoring the throughput requirements of high priority traffic of registered. STAs  215  and modifying one or more of the EDCA parameters to achieve desired throughput ratios across different ACs relative to the throughput requirements of the high priority traffic. The AP MAC controller  220  broadcasts the EDCA parameters in beacon frames to the STAs  215 . 
         [0046]      FIG. 2B  is a block diagram illustrating details of a WLAN  250  with traffic categories listed. In accordance with an embodiment of the present invention. As shown, The WLAN  250  includes an AP  255  and source and sink STAs  260   a - 260   e . As shown, STA  260   a  is a video source station; STA  260   b  is a best-effort source station; STA  260   c  is a best-effort sink station; STA  260   d  is a video sink station; and STA  260   e  is a source and sink voice station. Each STA MAC controller  260   a ,  260   b ,  260   c ,  260   d ,  260   e  is generally referred to herein as a STA MAC controller  260 , although each STA MAC controller  260   a ,  260   b ,  260   c ,  260   d ,  260   e  need not be identical. 
         [0047]      FIG. 3  is a block diagram illustrating details of an AP  300  (e.g., AP  205  or AP  255 ), in accordance with an embodiment of the present invention. The AP  300  includes a processor  305  (such as an Intel Pentium® microprocessor or a Motorola Power PC® microprocessor), memory  310  (such as random-access memory), a data storage device  315  (such as a magnetic disk), a computer network interlace  320 , input/output (I/O)  325  (such as a keyboard, mouse and LCD display), and a WiFi chipset  330 , each coupled to the communication channel  350 . The computer network interface  320  may be coupled to the computer network  210 . One skilled in the art will recognize that, although the memory  310  and the data storage device  315  are illustrated as different units, the memory  310  and the data storage device  315  can be parts of the same unit, distributed units, virtual memory, etc. The term “memory” herein is intended to cover all data storage media whether permanent or temporary. 
         [0048]    The memory  310  stores bridging software  345  that enables communications between the WiFi chipset  330  and the computer network interface  320 . The WiFi chipset  330  contains the AP MAC controller  220  and a network processor  335  coupled to a wireless antenna  340 . Details of the AP MAC controller  220  are described below with reference to  FIG. 4A . 
         [0049]      FIG. 4A  is a block diagram illustrating details of an AP MAC controller  220 , in accordance with an embodiment of the present invention. The AP MAC controller  220  includes a point coordinator module  405 , an AP distributed coordinator module  410 , an AP wireless medium communication module  415 , an AC monitoring module  420 , and an AC throughput adaptation module  425 . 
         [0050]    The point coordinator module  405  includes hardware, software and/or firmware that enables access to the wireless medium during the contention-free period (CFP) using point coordinated access. 
         [0051]    The AP distributed coordinator module  420  includes hardware, software and/or firmware that enables access to the wireless medium during the contention period (CP) using AC-sensitive distributed access, e.g., EDCA mode. The AP distributed coordinator module  420  forwards the AC-sensitive distributed access parameters to the STAs  215  in beacon frames. 
         [0052]    The AP wireless medium communication module  425  includes hardware, software and/or firmware that receives transmission frames from the point coordinator module  415  and/or the AP distributed coordinator module  420  and transfers the transmission packets to the network processor  335  for transmission by the wireless antenna  340 . 
         [0053]    It will be appreciated that during the initialization state, all STAs  215  register with the AP  205 . Thus, in one embodiment, the AC monitoring module  420  reads the source address of MAC packets for any transmission of any registered STA  215  to determine the traffic type (i.e., the corresponding AC) and its data rate. The AC monitoring module  420  may determine the corresponding AC by observing the duration of the channel busy state, which is limited by the TXOP parameter. The AC monitoring module  420  may estimate data rate by computing the average number of packets transmitted per unit time. By monitoring AC and data rates of the registered STAs  215 , the AC monitoring module  420  can determine the throughput requirements of the high priority traffic, e.g., VI traffic and/or VO traffic, of the registered STAs  215 . For example, IEEE 802.11g provides 54 Mbps in the physical layer, and about 30 Mbps (or 60% of 54 Mbps) in the MAC layer. If VI traffic requires about 20 Mbps (and assuming VO traffic is negligible relative to VI traffic), then in one embodiment the AC monitoring module  420  assigns the remaining 10 Mbps to BE and/or BK traffic, if there is no VI traffic at a given time, the AC monitoring module  420  may or may not reserve bandwidth, until such time that VI traffic is sent on the wireless medium. 
         [0054]    The AC throughput adaptation module  425  computes desired throughput ratios for the lower priority traffic, e.g., best-effort (BE) and background (Bk), relative to the high priority traffic, e.g., voice (VO) and/or video (VI). For example, if VI traffic is using 20 Mbps of a total possible 30 Mbps, then 10 Mbps can be assigned to BE and/or BK traffic. In one embodiment, the AC throughput adaptation module  425  may assign 8 Mbps to BE traffic and 2 Mbps to BK traffic. Thus, the ratio of BE traffic relative to VI traffic would be 8/20 or 0.4; and the ratio of BK traffic relative to VI traffic would be 2/20 or 0.1. 
         [0055]    Once the desired throughput ratios of high priority traffic are known, the AC throughput adaptation module  425  tunes one or more of the AC-sensitive contention-based (eg., EDCA) parameters (e.g., CWmin, CWmax, AIFSN and/or TXOP) across different ACs to allocate the remaining bandwidth to the low priority traffic. For example, in one embodiment, to achieve a throughput ratio 1:k across two ACs, namely, across high priority access class AC[HP] and lower priority access class AC[LP], the AC throughput adaptation module  425  may modify only one AC-sensitive contention-based parameter across the ACs, while maintaining the other AC-sensitive contention-based parameters as identical to each other. One skilled in the art will recognize that embodiments maybe developed to adjust AIFSN, CWmin, CWmax, TXOP and/or combinations of these parameters in various other manners. Four example embodiments are described below.
       1. Adjusting AIFSN: If AC[HP] and AC[LP] have identical CWmin, CWmax and TXOP values, then the AC throughput adaptation module  425  can achieve a desired throughput ratio of 1:k by adjusting AIFSN[LP] relative to a predetermined AIFSN[HP] as described below:       
 
         [0057]    To achieve the desired throughput ratios across different ACs, the AC throughput adaptation module  425  in one embodiment uses the AIFSN[HP] of AC[HP] as a baseline to determine the AIFSN[i] for lower priority AC[i]. That is, between AC[HP] and each AC[i], the AC throughput adaptation module  425  assumes a desired throughput ratio of 1:k i . For example, AC[VO] may be ignored and left with its default 802.11g values. Further, when compared to the throughput requirements of AC[VI], k i  for AC[BE] may be 0.4, and k i  for AC[BK] may be 0.2. Further, as shown in  FIG. 4B , the AC throughput adaptation module  425  defines AIFSN[HP]  455  as the corresponding AIFSN value for AC[HP], AIFSN[i]  460  as the corresponding AIFSN value for AC[i], and AIFSN_Lag[i]  465  as the difference between AIFSN[i]  460  and AIFSN[HP]  455 , i.e., AIFSN_Lag[i]=AIFSN[i]−AIFSN[HP]. 
         [0058]    If there are N 1  STAs  215  belonging to AC[HP] and N 2  STAs  215  belonging to AC[i], then the AP  205  throughput adaptation module  425  may apply the following relationship: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       ( 
                       
                         1 
                         - 
                         τ 
                       
                       ) 
                     
                     
                       
                         N 
                         1 
                       
                       × 
                       
                         AIFSN_Lag 
                          
                         
                           [ 
                           i 
                           ] 
                         
                       
                     
                   
                   = 
                   
                     
                       
                         N 
                         1 
                       
                       + 
                       
                         N 
                         2 
                       
                     
                     
                       
                         
                           N 
                           1 
                         
                         / 
                         
                           k 
                           i 
                         
                       
                       + 
                       
                         N 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where τ is the steady state probability of channel access for higher priority STAs computed for example as τ=2/(1+CWmin[HP]). Accordingly, the AC throughput adaptation module  425  computes AIFSN_Lag[i] in the following manner: 
         [0000]    
       
         
           
             
               
                 
                   
                     AIFSN_Lag 
                      
                     
                       [ 
                       i 
                       ] 
                     
                   
                   = 
                   
                     
                       log 
                        
                       
                         ( 
                         
                           
                             
                               N 
                               1 
                             
                             + 
                             
                               N 
                               2 
                             
                           
                           
                             
                               
                                 N 
                                 1 
                               
                               / 
                               
                                 k 
                                 i 
                               
                             
                             + 
                             
                               N 
                               2 
                             
                           
                         
                         ) 
                       
                     
                     
                       
                         N 
                         1 
                       
                        
                       
                         log 
                          
                         
                           ( 
                           
                             1 
                             - 
                             τ 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Since the above expression does not guarantee an integer value for AIFSN_Lag[i], the AC throughput adaptation module  425  considers a random AIFSN[i] mechanism for STAs  215  with AC[i] (according to a predetermined probability density function) and a fixed AIFSN[HP] value for STAs with AC[HP]. 
         [0059]    To effect the probability density function for STAs  21 . 5  with AC[i], the AC throughput adaptation module  425  assumes AC[i] STAs  215  choose AIFSN[i] value A with probability p and value A- 1  with probability 1−p. Accordingly, the expression for AIFSN_Lag[i]=AIFSN[i]−AIFSN[HP] can be rewritten as: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       AIFSN_Lag 
                        
                       
                         [ 
                         i 
                         ] 
                       
                     
                     = 
                     
                       
                         T 
                          
                         
                             
                         
                          
                         1 
                       
                       + 
                       
                         T 
                          
                         
                             
                         
                          
                         2 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     where 
                     , 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     T 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       log 
                        
                       
                         ( 
                         
                           
                             
                               N 
                               1 
                             
                             + 
                             
                               N 
                               2 
                             
                           
                           
                             
                               
                                 N 
                                 1 
                               
                               / 
                               
                                 k 
                                 i 
                               
                             
                             + 
                             
                               N 
                               2 
                             
                           
                         
                         ) 
                       
                     
                     
                       
                         N 
                         1 
                       
                        
                       
                         log 
                          
                         
                           ( 
                           
                             1 
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                             τ 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     3 
                      
                     a 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     T 
                      
                     
                         
                     
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                     2 
                   
                   = 
                   
                     
                       log 
                        
                       
                         ( 
                         
                           
                             1 
                             - 
                             τ 
                           
                           
                             1 
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                               p 
                                
                               
                                   
                               
                                
                               τ 
                             
                           
                         
                         ) 
                       
                     
                     
                       log 
                        
                       
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                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     3 
                      
                     b 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    The AC throughput adaptation module  425  uses a value p such that the resulting expression in (3) becomes an integer. Thus, p is a solution to the equation T 2 =1−frac(T 1 ), where frac denotes the fractional part of its argument. Letting f=frac(T 1 ), then 
         [0000]    
       
         
           
             
               
                 
                   p 
                   = 
                   
                     
                       1 
                       - 
                       
                         
                           ( 
                           
                             1 
                             - 
                             τ 
                           
                           ) 
                         
                         f 
                       
                     
                     τ 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Using the power series expansion, it can be shown that p≈f for τ&lt;&lt;1 (e.g., τ=0.2). Therefore, 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           D 
                           = 
                           
                             ⌈ 
                             
                               T 
                                
                               
                                   
                               
                                
                               1 
                             
                             ⌉ 
                           
                         
                       
                     
                     
                       
                         
                           A 
                           = 
                           
                             
                               AIFSN 
                                
                               
                                 [ 
                                 HP 
                                 ] 
                               
                             
                             + 
                             D 
                           
                         
                       
                     
                   
                   } 
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where ┌T 1 ┐ denotes the smallest integer greater than, or equal to T 1 . For example, assuming:
       CWmins HP =CWmin LP =15, CWmax HP =CWmax LP 31;   N 1 =N 2 =2; and   k i =0.5, AIFSN[HP]=2; using Eqs (3), (4) and (5) gives:   p=0.5349, D=2;   A=AIFSN[HP]+D=4; and   AIFSN[LP]=4 with, probability 0.5349 and 3 with probability 0.4651.   2. Tuning using CWmin: If AC[HP] and AC[LP] have identical TXOP and AIFSN values, the AC throughput adaptation module  425  can achieve a ratio of 1:k by adjusting CWmin of AC[LP] according to CWmin[LP]=integer(CWmin[HP]/k). If according to 802.11e, CWmin must be based on a particular formula, e.g., 2 n −1, then CWmin[LP] may he chosen as a value within 2 n −1 and nearest to integer(CWmin[Hp]/k).   3. Tuning using TXOP: If AC[HP] and AC[LP] have identical CWmin and AIFSN values, the AC throughput adaptation module  425  can achieve a ratio of 1:k by adjusting TXOP of AC[LP] according to TXOP[LP]=TXOP[HP]×k.   4. Tuning using TXOP, CWmin and AIFSN; If AC[HF] and AC[LP] have different sets of EDCA parameter values, the AC throughput adaptation module  425  can achieve a desired throughput ratio of 1:k between AC[HP] and AC[LP] by applying the following equations;
           a. Compute k_sub as:
               i.k_sub={TXOP[LP]/TXOP[HP]}×{CWmin[HP]/CWmin[LP]}   
               b. Compute k_rem as:
               i.k_rem=k/k_sub   
               
           c. Compute the parameters D, p and A using Eqs (3), (4) and (5) above but modified as follows:
           i. Compute τ using CWmin[HP] as: τ=2/(CWmin[HP]+1); and   ii. Substitute the value k_rem for k.   
               
 
         [0076]    Embodiments of the invention regulate throughput rates allocated to each AC, 
         [0077]    leading to better management of QoS and admission control for WLAN and mesh networks. 
         [0078]      FIG. 5  is a block diagram illustrating details of a STA  500  (e.g., STA  215  or STA  260 ), in accordance with an embodiment of the present invention. The STA  500  includes a processor  505  (such as an Intel Pentium® microprocessor or a Motorola Power PC® microprocessor), memory  510  (such as random-access memory), a data storage device  515  (such as a magnetic disk), input/output (I/O)  525  (such as a keyboard, mouse and LCD display), and a WiFi chipset  530 , each coupled to the communication channel  550 . One skilled in the art will recognize that, although the memory  510  and the data storage device  515  are illustrated as different units, the memory  510  and the data storage device  515  can be parts of the same unit, distributed units, virtual memory, etc. The term “memory” herein is intended to cover all data storage media whether permanent or temporary. 
         [0079]    The WiFi chipset  530  contains the STA MAC controller  225  and a network processor  535  coupled to a wireless antenna  540 . Details of the STA MAC controller  225  are described below with reference to  FIG. 6 . 
         [0080]      FIG. 6  is a block diagram illustrating details of a STA MAC controller  225 , in accordance with an embodiment of the present invention. The STA MAC controller  225  includes a point coordinator agent  605 , a STA distributed coordinator module  610 , and a STA wireless medium communication module  615 . 
         [0081]    The point coordinator agent  615  includes hardware, software and/or firmware that enables access to the wireless medium during the CFP using point coordinated access. 
         [0082]    The STA distributed coordinator module  620  includes hardware, software and/or firmware that enables access to the wireless medium during the CP using EDCA mode. The STA distributed coordinator module  620  receives the EDCA parameters from the AP  205 / 255  typically in a beacon frame, and uses the EDCA parameters to effect EDCA-based distributed coordinated access to the wireless medium. 
         [0083]    The STA wireless medium communication module  625  includes hardware, software and/or firmware that receives transmission frames from the point coordinator agent  615  and/or the STA distributed coordinator module  620  and transfers the transmission packets to the network processor  535  for transmission on the wireless antenna  540 . 
         [0084]      FIG. 7  is a flowchart illustrating a method  700  of tuning throughput across ACs, in accordance with an embodiment of the present invention. Method  700  begins with the STAs  215  in step  705  registering with the AP  205 . The AP  205  in step  710  monitors the channel and traffic to determine the following traffic parameters:
       highest priority traffic AC[HP];   the number L of active ACs;   the number Ni of STAs within AC[i]; and   the throughput ratio ki between AC[HP] and AC[i].
 
For AC[i], the AP  205  in step  715  computes the AIFSN values A, with its probability of access p, and A- 1 , with its probability of access 1−p, per equations (3)-(5) above. The AP  205  in step  720  increments for the next AC[i], and in step  725  determines whether all AC[I] have been managed. If not, then the AP  205  returns to step  715  to compute AIFSN values and probabilities of access for the next AC[i]. If so, then the AP  205  in step  730  broadcasts the computed set of AC-sensitive contention-based parameters over beacon frames. In another embodiment, the AP  205  in step  730  may broadcast a set of A and p values, which the STAs  215  use to compute the AC-sensitive contention-based parameters. The STAs  215  in step  735  receive the beacon frames and update the AC-sensitive contention-based parameters accordingly. Method  700  then returns to step  710  to continue monitoring the channel and traffic to determine whether the traffic parameters have changed, such that if changed perhaps more than a predetermined difference the AP  205  can adjust the A and p values and/or AC-sensitive contention-based parameters.
         
         [0089]    The foregoing description of the preferred embodiments of the present invention is by way of example only, and other variations and modifications of the above-described embodiments and methods are possible in light of the foregoing teaching. Although the network sites are being described as separate and distinct sites, one skilled in the art will recognize that these sites may be a part of an integral site, may each include portions of multiple sites, or may include combinations of single and multiple sites. The various embodiments set forth herein may be implemented utilizing hardware, software, or any desired combination thereof. For that matter, any type of logic may be utilized which is capable of implementing the various functionality set forth herein. Components may be implemented using a programmed general-purpose digital computer, using application specific integrated circuits, or using a network of interconnected conventional components and circuits. Connections maybe wired, wireless, modem, etc. The embodiments described herein are not intended to he exhaustive or limiting. The present invention is limited only by the following claims.