MXPA06007744A - Packet scheduling in a wireless local area network - Google Patents

Abstract

A method for scheduling packets in a wireless local area network begins by mapping a packet to an access category (AC) based on a user priority of the packet. The packet is assigned to a traffic flow (TF) in a station based on the AC of the packet. A packet from the TF is placed into a transmission queue for the AC. A packet from the transmission queue is selected based on a quality of service-based contention resolution function, and the selected packet is transmitted.

Description

ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), For two-letter codes and other abbreviations, refer to the "GuidEuropean (AT, BE, BG, CH, CY, CZ , DE, DK, EE, ES, FL ance Notes on Codes andAbbreviations "appearing at the begin- FR, GB, OR, HU, IB, IS, 1T, LT, LU, MC, NL, PL, PT, RO, ning of regular issue of the PCT Gazette SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, Cl, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG ). Published: - without intemational search report and to be republished upon receipt of that report PROGRAMMING OF PACKAGES IN A LOCAL AREA WIRELESS NETWORK FIELD OF THE INVENTION The present invention relates in general ... to wireless communication systems, and in particular, to the programming of traffic flow packets in wireless local area networks (WLANs).

BACKGROUND In an environment based on the 802. lie standard, the enhanced distributed coordination function (EDCA) classifies traffic flows into access categories (ACs) that reflect the priority of the application carried by each traffic flow. The different arbitrage space parameters between frames (AIFS), minimum containment window (C min) and maximum containment window (CWmax) are assigned per traffic flow according to their AC. The AIFS is the period of time a station waits (STA) after receiving confirmation from an access point (AP) that a previously transmitted packet was received. A higher priority AC has a lower AIFS than a lower priority AC, so that higher priority traffic has a shorter waiting time before accessing the channel. The CWmin and CWmax values define the lower and upper limits for a containment window, which is used during a backspace procedure. The EDCA helps ensure that higher priority traffic flows have a better chance of gaining access to the channel through favorable configurations of AIFS, CWmin and CWmax. The 802. lie standard specifies the containment and retraction mechanism between several ACs. However, the programming in the AP between different traffic flows (belonging to different STAs) within the same AC is not specified by the standard, and is left to the implementation of the AP.

THE INVENTION A method for programming packets in a wireless local area network begins by mapping a packet to an access category (AC) based on a user priority of the packet. The packet is assigned to a traffic flow (TF) in a station based on the packet's AC, a TF packet is placed in a transmission queue for the AC. A packet from the transmission queue is selected based on a contention resolution function based on the quality of service, and the selected packet is transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood through the following description of a preferred embodiment, given by way of example and to be interpreted together with the accompanying drawings, in which: Figure 1 is a flowchart that shows a method for programming packets according to the present invention; Figure 2 is a diagram showing the functionality of the EDCA with a contention resolution function based on the QoS operating in multiple traffic flows; Figure 3 is a flow chart of the contention resolution function operating within the same AC; and Figure 4 is a diagram of the containment solution function shown in Figure 3.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention implements an internal containment resolution function based on the quality of service (QoS) in the AP. The QoS-based function operates according to the AC to resolve a contention between the multiple streams of traffic flow within the same AC. The containment resolution function is triggered when there are packets in two or more traffic flow queues in the same AC, and both queues try to access the channel f * n at the same frame transmission time. The output of the containment resolution function is the internal contention priority for each AC, which is the priority used to access the channel. The operation of the QoS function based on the delay 100 is shown in Figure 1 and is described in the context of the operation of the EDCA. The EDCA function supports four ACXs. Eight different user priorities (OPs) are mapped to these four ACs as indicated in Table 1. Table 1: User Priority for the Access Category mapping A packet that will be transmitted by an STA will be attached to an AC based on its ÜP (step 102). The mapping function ensures that the ÜPs are mapped to the respective ACs, and that the packets of the different traffic flows are routed to their respective queues in their AC. In the 802. lie standard, an STA can have one or more traffic flows and the traffic flows can be distributed among the ACs or grouped in the same AC, depending on the application run from the STA and the number of simultaneous sessions of the same application. For the purposes of implementation, each STA is limited to having a maximum of four traffic flows and each traffic flow supports a different application. It should be noted that an STA can have more than four traffic flows and can support simultaneous sessions of the same application; the present invention would still operate in the same way in such circumstances. Therefore, an AC can support up to N traffic flows, where N is the number of STAs in the system. An AC may have no traffic flows if none, and the STAs are running an application that belongs to that AC. ' A packet is assigned to a traffic flow in an STA based on its AC (step 104). The packets of each traffic flow are placed in a transmission queue for the corresponding AC (step 106). A packet of the transmission queue of each CA is selected by the containment resolution function based on the QoS, based on the transmission rate and delay requirements of the CA (step 108), this function is described in more detail in relation with Figures 3 and 4). An attempt is made to transmit a selected packet (step 110) and it is determined whether a transmission collision will occur with another packet (step 112). If np a collision would occur, then the selected packet is transmitted (step 114) and the function ends (step 116). If a collision would occur with another package (step 112), then the highest priority packet is transmitted (step 120). The value of the containment window (CW) for the lower priority packet is compared to the Cwmax value for the AC associated with that packet (step 122). If the value of CW e's lower than CWmax, then the CW value is updated as as indicated by Equation 1 (step 124).

CW = ((CW + 1) x 2) - 1 Equation (1) once the CW value is updated or if CW already sp finds in CWmax (step 122), then the lower priority packet enters a backward mode for a period equal to CW (step 126) and an account timer is started regressive Once the countdown timer reaches zero (step 128), it is determined whether the channel is free by detecting multiple access by carrier detection avoiding collisions (CSMA / CA) (step 130). If the channel is not free, then the function returns to step 124 to reset the CW value and reset the countdown timer. If the channel is free, then the lower priority packet is transmitted (step 132) and the function ends (step 116). Next, function 100 will be described in relation to Figure 2, which shows an example of an EDCA implementation model that has four STAs, where each of them runs four different applications, mapped to different ACs, thus creating a flow of traffic for each STA in each AC. A packet is assigned to a traffic flow in an STA, based on its CA, for example, a second traffic flow (TF_2) from station B (STA_B) is in AC_2. The packets of each traffic flow are inserted into a separate transmission queue, and the containment resolution function based on the QoS designates a packet of each AC to transmit them. Once a packet is selected from an AC, for example, AC_2, and ready for transmission (ie, it is not in the reverse mode and detects that the channel is free), then it will attempt transmission on the channel. If there is another packet ready for transmission from another AC, for example, AC_4, this produces an internal collision between the ACs. In this case the AC_2 package (lower priority) will allow the AC with the highest priority (AC_4) the right to access the channel and transmit. AC_2 updates its CW [AC_2] to the value ((CW [AC_2] + 1) x 2) - 1 or leaves the CW value unchanged if CW [AC 2] has already reached Cwmax [AC 2].

The packet of AC_2 begins, then, a backward procedure, and decreases its countdown until it reaches zero. If then the channel is free, the packet attempts the transmission. As long as the AC_2 packet is not transmitted, the contention resolution function based on the QoS will not be triggered for AC_2 and no other packet will be designated for transmission for a category AC_2. If the countdown timer reaches zero for the standby packet in AC_2, and there are no other packets with which the AC-_2 packet can collide, then AC_2 will transmit that packet. In the event of a collision, you will have to start a new backing procedure to update your CW [AC_2] according to the value ((CW [AC_2] + 1) x 2) - 1. After a successful transmission, an AC that has just sent the final transmission within its allowable transmission opportunity (TXOP), will update its CW [AC] value and initiate a rollback procedure for the next packet and be designated regardless of the occurrence of a collision with a higher priority AC. A TXOP is a point in time at which an STA can begin to transmit frames with a given duration. During a TXOP, an STA can transmit as many frames as possible in the TXOP, whose length is set according to the traffic class (TC) associated with the data. The TXPA of the EDCA must not exceed the limit of the TXOP warned by the AP. This is necessary to ensure that the highest priority ACs do not continuously limit the lower priority ACs in the AP when they have something to transmit, and that the prioritization is carried out through the favorable setup values of CWmin [AC] , CWmax [AC] and AIFS [AC]. In an EDCA, a traffic flow will initiate a rollback procedure in the following three cases: 1. Due to an internal collision with larger ACs. 2. Due to an external collision with another STA that shares the wireless channel. -.s 3. After the final transmission within the assigned TXOP after designating another packet to transmit. If there is only one traffic flow queue at a given AC, then the containment resolution function based on the QoS will not be effective, since there are no other queues with which to contend. Containment Resolution Function Within each queue, a Priority index is calculated based on the Delay and Data Speed criteria. The calculation of the Data Rate index takes into account the instantaneous data rate used to transmit the packet. A higher data rate requires less average time and, therefore, priority is given to it. This improves overall system performance, but may increase the delay for users with low data rates. The calculation of the Delay index has e > n counts the delay of the first packet in each queue (that is, the time the packet has spent in the queue) and the size of the queue, to reflect the QoS requirements for each traffic flow. Then, the packet with the highest Priority index (a combination of the Data Rate and Delay) within the same AC is programmed to compete for transmission with other ACs. Figure 3 shows a flowchart of a containment resolution function 300, which determines the next packet to be programmed based on the estimated data rate and the current delays incurred by the packet. The contention resolution function 300 is also shown by means of a diagram in Figure 4. There is a queue for each AC and it is indexed with "n". In each queue, a Priority index is calculated for each packet based on the Delay and Data Speed criteria. The Delay index includes parameters dependent on the AC. The Data Rate index for each queue within the ACn is calculated according to Equation 2 (step 302): data rate data Rate of Data Rate = Maximum data rate Equation (2) where the maximum data rate is the maximum data rate allowed by the applicable standard. For example, in the 802.11b standard, the maximum data rate is 11 Mbps and in 802.11g the maximum data rate is 54 Mbps. The Delay rate of each queue within ACn is described in Equation 3 (step 304) : Delay index = (A [ACn] x First_Pkt_Delayn (normalized) + (B [ACn] x Queue_Sizen) + (C [ACn] x Avg_Pkt_Delayn (normalized) Equation (3) where First_Pkt_Delayn is the delay experienced by the first packet in ACn, Queue_Sizen, is the size of ACn and Avg_Pkt_Delayn is the moving average of a delay of the ACn packet, with respect to M packets. A, B and C are weighting factors for each CA for the package delay, the size of the queue and the average delay of the packet, respectively.

The initial values for the weighting factors that can be applied to all the ACs as a starting point are: A = 0.4, B = 0.3, and C = 0.3. The values of A, B and C can be adjusted during the operation by monitoring the average tail size. If the size of the queue increases too much, the value of C can be increased and the value of A or B decreased at the same time. Alternatively, according to the CA, different configurations can be used for the three weighting factors, which emphasizes the different aspects of the QoS of the traffic carried by each CA and more efficiently determines the priority to access the channel. The first and third terms of the Delay index equation are normalized to an integer value so as not to be eclipsed by the second term, which is the size of the tail. The tail with the calculation of the highest Delay index will have a higher probability of obtaining access right to the channel, according to the calculation of the Priority index (step 306): Priority index = (Alpha x Data Speed index ) + (Beta x Delay Index) Equation (4) where Alpha is a weighting factor to reduce the impact of the data transmission rate and Beta is a weighting factor to reduce the impact of the delay. In one embodiment of the present invention, Alpha = 0.5 and Beta = 0.5. These values can be adjusted over time by monitoring the number of packets that experience a delay of X seconds. If the number of packages exceeds 10% (this value can be configured), then adjustments can be made to the alpha and beta weightings, for example, decrease Alpha and increase Beta. The first packet in the traffic flow with the highest Priority index value is selected for transmission (step 308) and the function ends (step 310).

While the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and features. elements of the present invention. Although specific embodiments of the present invention have been shown and described, many modifications and variations may be made by the person skilled in the art without departing from the scope of the invention. The above description serves to illustrate and in no way limit the particular invention.

Claims (13)

1. CLAIMS 1. Method for programming packets in a wireless local area network, characterized in that it comprises the steps of: mapping a packet to an access category (AC) based on a user priority of the packet; assign the packet to a traffic flow (TF) in a station based on the AC of the packet; place the TF packet in a transmission queue for the CA; select a packet from a transmission queue based on a containment resolution function based on the quality of the service; and transmit the selected package. Method according to claim 1, characterized in that the selection step includes the steps of: calculating a priority value for each TF; and selecting a first packet in the TF that has the highest priority value. Method according to claim 2, characterized in that the priority value is calculated according to the equation: Priority index = (Alpha x Data Speed Index) + (Beta x Delay index) where Alpha and Beta are weighting factors, the Data Rate Index is based on an instantaneous data transmission rate, and the Delay Index is based on the delay of the first packet in the transmission queue and the size of the queue. 4. Method according to claim 3, characterized in that the Data Rate Index is calculated according to the equation: Data transmission rate Data rate index = Maximum data rate where the maximum data rate is the maximum speed of data. data allowed on the network. Method according to claim 3, characterized in that the Delay index is calculated according to the equation: Delay index = (A [ACn] x First_Pkt_Delayn, (normalized) + (B [ACn] x Queue_Sizen) + (C [ACn] x Avg_Pkt_Delayn, (normalized)) where A is a weighting factor for the delay of the packet, First_Pkt_Delayn is the delay experienced by the first packet in ACn, B is a factor of weight for the size of the queue, Queue_Sizen is the size of ACn, C is a weighting factor for the average delay of the packet, and Avg_Pkt_Delayn is the moving average of the delay of the ACn packet with respect to a predetermined number of packets . Method according to claim 3, characterized in that Alpha and Beta are adjusted dynamically. Method according to claim 6, characterized in that Alpha and Beta are adjusted based on the number of packets experiencing a predetermined delay. 8. Method according to claim 1, characterized in that the transmission step includes the detection of whether a transmission collision occurs with another packet. 9. Method according to claim 8, characterized in that if no collision occurs, then the selected packet is transmitted. Method according to claim 8, characterized in that if a collision occurs, the steps of: determining which package has the highest priority are carried out; transmit the highest priority package; execute a backspace procedure for the lower priority package; and transmit the lower priority package. Method according to claim 10, characterized in that the execution step includes: determining a value of the containment window for the lower priority packet; update the value of the containment window s: i is less than a maximum value; Wait for a time equal to the value of the containment window. Method according to claim 10, characterized in that the lower priority packet is transmitted if the channel is free. Method according to claim 12, characterized in that if the channel is not free, another retraction procedure is executed; for the lower priority package.