TW201029386A - Fixed window Backoff method capable of QoS guarantee for Wireless LANs - Google Patents

Abstract

The present invention discloses a Fixed Contention Window Backoff method capable of QoS guarantee for Wireless LANs. The method also comprises steps of applying a tuning procedure for system parameters. The tuning procedure determines the optimal values for the minimum contention window size (CWmin) and the transmission opportunity (TXOP). With those optimal parameters, the Fixed contention window Backoff method has better performance for wireless LANs than traditional binary exponential backoff method.

Description

201029386 VI. Description of the Invention: [Technical Field] The present invention relates to a wireless medium access control (medium deduction ""control 'MAC" method, and more particularly to a wireless local area network with a service quality assurance fixed window retreat method It can be applied to the wireless local area network to achieve both the quality of service (QoS) and the high channel usage (the utility of ^Utilization). [Prior Art] Wireless local area network refers to the structure without using physical lines. Regional network, most of the current wireless local area network technology uses radio waves (rf: constitutes a communication network for the transmission medium. The basic service area of the wireless local area network (Basjc Servjce) usually contains a wireless access Point (Access p〇int, referred to as Ap) and a limited number of mobile stations (Mobile Station, such as: wireless network card, pDA, notebook computer, etc.) wireless local area network system uses wireless channels to connect various network members Under the standard of WLAN defined by EEE, each network member can be contacted, communicated, and quickly Exchange of data, data, files and audio and video information. Due to the maturity of radio technology, wireless networks are booming and "other-side" with the development of various applications, users: the need for bandwidth More (4) 'So how to effectively improve the bandwidth to become the focus of the research and development of the second generation of information industry, in addition to the progress of the physical layer transmission speed, "access control design is also a big time. Because of the various networks All members of the road use _wireless media to transmit data, 201029386. Therefore, it is necessary for each network member to abide by the same agreement to coordinate the access of each network member to this media. Generally, the wireless network under the IEEE802.1 1 standard is in the media. The access mode used by the access control (MAC) is the access mode of the "Distributed Coordination Function" (DCF). In this DCF mode, each station detects multiple access/collision avoidance based on a carrier. (Carrier Sensing Multiple AccesS// Collusion Avoidance, CSMA/CA for short) to access the wireless media. • According to the above agreement, when Before sending the data, the station A will detect whether the current wireless medium is interposed (idle, which means to detect whether other stations are already transmitting in the wireless medium). If the wireless medium is idle, the station A randomly selects a retreat. (backoff) time starts counting down and continuously detects wireless media. At the end of the back-off time, if the wireless medium still sets 'representing the station A' has access to the media, it can start to send its frame ( Frame). Conversely, if station A has been occupied by the wireless medium before the end of the countdown (meaning that other stations have started to send frames), then station A will participate; east will count down; until station A again (four) to the wireless medium is in The idle L station σ A will again start the reciprocal of the backoff period to continue to gain access to the wireless medium. In other words, the stations coordinate each other to the wireless medium in an independent random selection-rebate time manner. Access rights, the station with a shorter retreat time will end the countdown first, and first obtain access to the media to start sending data; if there are more than two stations at the same time the end of the countdown will send data at the same time and cause collision (4)| Isj〇n), a retransmission mechanism will be started. According to the carrier detection multi-access/collision avoidance protocol 5 201029386, the decision of the back-off time will affect the performance of the entire wireless network. If the back-off time is long, the probability of collision will decrease. However, when the wireless channel has too much interlacing, its usage rate decreases. Conversely, if the retreat time is short, the probability of collision will increase, and the time of retransmission will increase, which will also reduce the effective usage of the channel. In order to reduce the occurrence of repeated collisions, the current 8〇2彳1 standard mostly adopts the binary exponential retreat mechanism (Bjnary Exp〇nentia| Back〇ff, referred to as BEB), which will be used each time when the return time is selected. A value is selected on average, where CW is called the current contention window. When a station wants to start transmitting data, CW will set a minimum value of CWmin, and then start the withdrawal mechanism. When the countdown ends, the data will be transmitted. If it succeeds, it will start to prepare the next data. If a collision occurs, it will start the retransmission mechanism, multiply the value of CW, and then start counting down. After each collision, the selection range of the retreat time CW is doubled. The chance of selecting the same retreat time will be effectively reduced. If the collision continues, the value of CW continues to multiply until a maximum value CWmax is ©. After the maximum value Cwmax, if the collision continues, the value of CW remains unchanged. 'Recursively once per collision. If the number of retransmissions reaches the upper limit of one retransmission (R) or collision, the data will be discarded. Since the job mode that has to be re-competitive after each piece of data is sent out is inefficient, so in the new IEEE 802.11-2007 standard, a transmission opportunity has been developed to improve network performance (Trsmsmissi〇n

Opportunity (referred to as TXOP) function, the system will preset a time value of τχορ. When a station grabs the access right of the wireless medium, it can access the wireless media to the maximum TXOP time by 6 201029386, thereby improving The effectiveness of the network. With the advancement of network services, in addition to high-bandwidth, quality of service (QoS) guarantees are becoming more and more important. Therefore, an enhanced distributed channel access mode is also defined in the IEEE 802.11-2007 standard. Referred to as EDCA), although it can provide four different types of services, it can only make the difference between different services 'can not provide a real guarantee. In addition, because each service also directly competes with the wireless media, in some cases it will increase the collision probability and reduce the channel usage. SUMMARY OF THE INVENTION It can be seen from the above description that the media access control of the IEEE 802.1 1 wireless local area network accesses the media according to the carrier detection multiple access/collision avoidance protocol, and generally adopts a binary exponential backoff mechanism (Bjnary Exp〇nentj). ^ (7)

In order to reduce the chance of re-collision, but it will cause an increase in delay, it is difficult to achieve good service quality assurance, and the minimum competition window and transmission opportunity does not provide a parameter setting recommended value. There is a problem in the present invention that provides a wireless area network with a fixed quality window for service quality assurance, and a method for dynamically retreating, which can dynamically adjust the size of the minimum bid window and the transmission opportunity π.. to the most The value of the mind is such that the wireless network reaches the operating point of the farmer's to achieve the guarantee of service quality. In order to achieve the above-mentioned target service quality assurance, the technical means used to include the following steps 'to make the wireless local area network fixed window withdrawal method by - communication device, 201029386 ready to transmit data; according to a best minimum competition window The parameter CWmin and the transmission opportunity parameter TXOP randomly select a back-off value according to the uniform distribution in the [〇, cWmin-1] interval; reduce the back-off value by one unit when idle for one time slot time; start after the return value is reduced to zero unit The data can be transmitted continuously, and the TXOP time can be continuously transmitted. It is judged whether the data is successfully transmitted. If it succeeds, the data transmission is terminated, and the above-mentioned preparatory data transmission step is executed again to transmit the next data. Otherwise, the next step is performed; Exceeding a predetermined number of retransmissions R, if yes, proceeding to the next step 'or vice versa, using the same minimum contention window parameter CWmin to perform the aforementioned step of randomly selecting the retreat value; and discarding the current data and re-executing the aforementioned preparatory transmission data step For the transmission of the next data. The minimum competition window parameter CWmin and the transmission opportunity parameter ❹TXOP described in the month are derived by performing a parameter setting method, which includes the following steps: providing a collision probability parameter P, a given maximum delay time value D And a further loss probability parameter P1_, a given number of communication devices N, a minimum transmission opportunity parameter TXOPmin of an initial value of 188, and a variable maximum transmission opportunity parameter TX〇pmax of an initial value; according to the collision probability The parameter P respectively calculates the probability r of a station at random time transmission and a minimum contention window parameter cWmin; according to the minimum transmission opportunity parameter TXOPmin, the maximum transmission opportunity becomes 8 201029386, the random number of the competition TXOPmax, the number of retransmissions R, the random transmission Probability r and most ^

The window parameter Cwmin calculates a distribution representing the time difference d of two consecutive transmission opportunities; B is based on the premise that the random variable d is greater than the maximum delay 小于 and the probability of the failure rate is PL, the minimum transmission opportunity variable Tx 〇 Pm 爹The long-attack big-reading opportunity variable TXOPmax finds out when the collision probability parameter is the best transmission opportunity parameter TXOP. p # #

Therefore, the present invention can obtain the left ideal minimum competition window parameter and the transmission opportunity parameter by changing the collision probability parameter to p, and each station & the most parameter setting is set to match the fixed window retreat mechanism, and the wireless network is effective. The balance between service quality assurance and maximum channel usage. P. [Embodiment] The embodiments of the present invention will be described in conjunction with the drawings to make the foregoing description more specific. Before clarifying the fixed window retreat mechanism of the present invention, the conditions for satisfying the quality of service (Qos) are specifically defined: the wireless local area network includes a total of N communication devices, as shown in the first figure. The communication device comprises a wireless access point (Red (10) Point) (1) and a plurality of stations (2) 'The wireless access point (1) sets the same transmission according to the number of communication devices n and the quality of the user's service quality. Opportunity time is given to each station (7). Among them, the demand for service quality is: in the worst case (that is, the wireless access point (1) and each station (, 2) continue to have f material to be sent), and a communication device transmits τ twice in succession. The time difference of ρ is a random variable d. It is hoped that the wireless network can guarantee that the probability that the random variable d is greater than a predetermined 201029386 maximum delay D is less than a loss probability PL, that is, p(d>D)$ Ρ|_. Therefore, in order to meet the service quality requirements, it is necessary to control the probability of collision and avoid the delay caused by frequent collisions. According to the invention, the fixed window retreat method of the present invention applies a parameter setting method, so that the wireless access point (1) calculates an optimal and fixed minimum contention window parameter CWmin and an optimal one according to a parameter setting method. Transfer the opportunity parameter TXOP and pass these two parameters to each station (2). The wireless access point (1) and each station (2) operate under the fixed window and the retreat method under these parameter settings, which will enable wireless The local area network effectively balances service quality assurance with optimal channel usage. The following is a detailed description of the fixed window retreat method of the present invention. Please refer to the first figure as shown in the following figure: 'Include the following steps: Prepare to transmit data (1 〇 1); Select the return value (102) to make the communication device according to the best one. The minimum competitive window parameter CWmin is randomly selected from the [O.cWmin-l] interval according to a uniform distribution, wherein the communication device can be a benefit line β access point (1) or a station (2); The value of the concession (103) 'Let the communication device pass idle time slot time (the slot of the wireless network), the depreciation value is reduced - the unit; „ start transmitting data (104), so that the communication device When the concession value is reduced to zero soap level, the data is transmitted, and the data can be transmitted continuously for up to three consecutive times to determine whether the data is transmitted successfully. In step (101), the delivery is successful (1 05), so that the communication is made. If the device determines that the pen is successful, the data transmission is terminated (108) and the data is again executed. Otherwise, the next step is performed; 201029386 determines whether the number of failures exceeds the number of retransmissions (106), so that the communication device judges Whether the number of failures exceeds a predetermined number of retransmissions R, if the next step is performed, otherwise the same minimum contention window parameter cw is used to return to step (102); and the pen data (107) is discarded, The communication device discards the current data when the number of failures exceeds the number of pre-retransmissions R, and re-executes the step (1〇1) to transmit the next data. For the purpose of increasing the channel usage rate, although the transmission opportunity is increased ❹

The channel utilization rate can be increased, but the delay will increase and the service quality requirement may not be met. Therefore, the transmission opportunity time must be controlled to the optimal value to find the maximum transmission opportunity time under the service quality requirement. The optimization setting mentioned in the foregoing steps is to obtain the optimal minimum contention window parameter and transmission opportunity parameter by using the foregoing parameter setting method. Therefore, please refer to the third figure, the parameter setting method includes the following steps: Provide Ρ and, D, PL, Ν, TXOPmin and TXOPmax parameters (200) 'provide a collision probability parameter p, a given The maximum delay time value D, ', σ疋's loss probability parameter PL·, a given number of communication devices Ν, an initial value variable minimum transmission opportunity parameter TX〇pm丨η and one and the initial value Change the maximum transmission opportunity parameter TX〇Pmax; Calculate the probability of random time transmission r and the minimum competition window parameter CWmm(2Q1) 'This embodiment# is based on the collision probability parameter ρ according to the public----CW . (2-τ )(1-2ρ)α-^+ι) Equation τ = 1~Ν4(ϊ^ρ) and m A1 —(10))(1_心ΗΗ) Calculate the probability of 11 201029386 station transmitting at random time respectively r and a minimum contention window parameter CWmin; taking TXOP = (TXOPmin+TXOPmax)/2 (202), that is, taking the intermediate value of the minimum transmission opportunity parameter TXOPmin to the maximum transmission opportunity parameter Tx〇pmax as the current transmission opportunity parameter TX0P; The distribution of random variables d (203) is based on the number of retransmissions r, the random transmission probability τ The minimum contention window parameter CWmin and the current transmission opportunity parameter TXOP are used to calculate the distribution of the random variable d; the φ distribution of the random variable d can be calculated by reference [1][2] ([1] : A. Banchs, P. Serrano and A. Azcorra, End-to-end delay analysis and admission control in 802.11 DCF WLANs,,,

Compute Communication, vol. 29, issue 7, pp 842-584, April 2006. [2] : Hai L. Vu and Taka Sakurai, “Accurate Delay Distribution for IEEE 802.1 1 DCF,” IEEE Communication Letters, vol. 10, no 4, 2006.); Calculate P(d>D)(204) ' Calculate the probability p(d>D) of the random variable d greater than the maximum delay φ D; determine whether P(d>D) is greater than PL(205) If the probability P(d>D) is greater than the lost probability parameter PL, it indicates that the current TXOP is too large and needs to be small, so that the aforementioned maximum transmission opportunity parameter TXOPmax is equal to the value of the current transmission opportunity parameter TXOP and the maximum transmission opportunity parameter is used. TXOPmax returns to step (202) to continue searching for the ideal TXOP, and vice versa. It is judged whether the difference between P(d>D) and PL is small enough (206), that is, P(d>D) is judged. Whether the difference of PL is less than a specific value, if it is less than the specific value of 12.201029386, the next step is performed, otherwise the current TXOP is too small and needs to be enlarged, so that the minimum transmission opportunity parameter Txopmin is equal to the current transmission opportunity parameter TX0P. The value and return to step (2〇2) to continue to find the ideal TX0P; The best TXOP value (207) is obtained, and τ χ〇 ρ at this time is the optimal transmission opportunity parameter 当 when the collision probability parameter is Ρ. The foregoing steps (204) to (207) are based on the premise that the probability that the random variable d is greater than the maximum delay D is less than the loss probability parameter pL, and is searched between the minimum conveyor and the parameter Tx〇Pmm and the maximum transmission opportunity parameter TX〇Pmax. An optimal transmission opportunity parameter TXOP. When applied to an actual wireless local area network system, the setting of the aforementioned collision probability parameter P value can be determined by the user using the above parameter setting method in a suitable P value range after giving the missing probability parameter pL value. The optimal transmission opportunity parameter τχ〇ρ corresponding to the value is calculated according to the obtained transmission opportunity parameter ΤΧ〇Ρ (4) y, (4) comparing the channel usage rate #, then the optimal Ρ value can be known. ® For example, given the aforementioned maximum delay parameter D = 4Gms, the missing probability parameter two L-0.01, the number of retransmissions R = 6, and the collision probability parameter ρ is 〇 〇 〇 π into the above steps, which can be obtained as shown in the fourth figure. The relationship between the collision probability and the channel usage rate shows that the transmission is found to be the best when the number of communication devices is too large, and the collision machine _ > The opportunity parameter TXOP is the best value. In the actual application, the optimum P value corresponding to the missing probability parameter can be calculated in advance, and the matching P value of the parameter is calculated in advance, and then the matching combination of the parameters is stored in the wireless access point (1) to enable wireless storage. Take the point (1) under the PL reset 13 201028386, you can immediately get the best P value by matching the matching combination of the parameters stored in the π ^ iw. As shown in the above description, the operating procedure of the parameter setting of the wireless access point (1) under the system can refer to the fifth figure: when the administrator sets the required loss rate at the wireless access point (1) When the parameter PL is (300), the wireless access point (1) will get the best value (〇彳) wireless access point according to the matching combination of the stored k β and the number (1) according to the best ρ value. You can use the above parameters "and the method to get the best minimum competition window parameter CWmin and conveyor❹

The parameter TXOP will be transmitted, and the obtained parameters will be transmitted to each station (7) setting, after which all communication devices (ie, wireless access point and station) will transmit data according to the aforementioned fixed window T method; when a new station is added or the original station Leave % (302) 'Because the number of communication devices changes, the wireless access point (1) will recalculate the optimal τχ〇ρ and CWmin (303) according to the aforementioned parameter setting method; when the wireless access point (1) judges When the new station joins, causing the new TXOP to be too small to transmit the maximum packet (304), the wireless access point (1) will reject the joining of the new station (305), otherwise the wireless access point will be re-established. The best TX0P and CWmin are set to each station (306). ° The above channel usage rate is calculated by a formula: "(1 - Plr)Te + P^Psf^pjir^r ancient ten counts, where Te is the time of the wireless network basic unit S|〇t; ts is The time required to successfully transmit TX0P, Tc is the time wasted by the collision; ρ. The probability of transmitting at least one station in a slot is ητ{\-τ)Ν'χ eight in the case of at least one station in a certain slot.

Ps: - probability of station transmission, ie 201029386 The fixed window retreat mechanism of the present invention is different from the commonly used binary exponential depreciation method. After determining the optimal minimum competition window CWmin size, the fixed no longer changes, in the case of Q〇S Under the request, the channel utilization rate of the present invention and the binary exponential retreat mechanism can be referred to the fifth figure. It can be clearly seen that the effectiveness of the fixed window retreat mechanism of the present invention is greater than the standard binary exponential retreat mechanism. If the experiment is carried out with different numbers of communication devices, the difference between the two will be more obvious. In summary, the present invention provides a fixed window retreat mechanism for the media access control layer of the EEE 8〇2彳彳 wireless network β, and in view of the prior art, there is no minimum contention window and transmission. The opportunity provides a parameter setting method. Therefore, the present invention simultaneously provides a parameter setting method. Regardless of the number of communication devices, the best collision probability p can be found by giving the missing probability parameter pL, and the optimal minimum is obtained. The competition window CWmin and the transmission opportunity parameter TX0P enable the communication device of the wireless local area network to operate with the fixed window retreat mechanism under these ideal parameter settings, which can effectively balance the quality of service guarantee (Qos) and the maximum channel usage rate (Channel Utilization). ). [Simple description of the diagram] The first picture: a schematic diagram of the member structure of a communication device of a wireless network. First Figure: Flow chart of the fixed window retreat method of the present invention. Second figure: The parameter setting flow chart of the fixed window retreat method of the present invention. Figure 4: The relationship between the collision probability and the channel utilization rate of the present invention under the number of different communication devices. 15 201029386 FIG. 5 is a flow chart showing the operation of parameter setting by applying the wireless access point (1) of the present invention. Figure 6: Comparison of the present invention and the binary exponential depreciation method in terms of collision probability and channel usage. [Main component symbol description] (1) Wireless access point (2) Platform

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Claims (1)

201029386 VII. Patent application scope: 1 · A wireless local area network fixed service window retreat method with service quality assurance, which is executed by a communication device, which comprises the following steps: preparing to transmit data; according to the best minimum competition window parameter cwmin And the transmission opportunity > number TXQP in [. (4) Coffee-"Interval: randomly select a return value according to the uniform sentence distribution; reduce the return value by one unit when idle for one slot time; start transmitting data after the return value is reduced to zero unit, and can continuously transmit TXOP time continuously ; to determine whether the data is successfully transmitted, if successful, end the data transfer and perform the above steps to prepare the transfer data to transfer the next data, otherwise proceed to the next step; / / / break the number of failures exceeds - retransmission The secondary IR, if it is exceeded, enters the light-down step. Otherwise, the same minimum contention window parameter cw_ is used again to perform the aforementioned random selection of the return value; the current data is discarded and the aforementioned preparatory data transmission step is performed again to perform the next step. The transmission of a piece of data. 2. If the wireless area network has a fixed window retreat method for service quality assurance as described in the patent, the minimum contention window parameter CWmin and the transmission opportunity parameter are set by the uranium system. According to the method, the parameter setting method includes the following steps: providing a collision probability parameter D, —, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Opportunity parameter dare TXOPmin and an initial value of 17 201029386 . Variable maximum transmission opportunity parameter TX0Pmax; According to the collision probability parameter p, the probability T of a station at random time transmission is calculated: and a minimum competition window parameter CWmin ; take the intermediate value of the minimum transmission opportunity parameter Txopmin to the maximum transmission opportunity parameter TXOPmax as the current transmission opportunity parameter τχ〇ρ; according to the number of retransmissions R, the random transmission probability τ, the minimum competition window parameter CWmin and the current transmission opportunity parameterΤχ〇 ρ is calculated—the distribution of the random variable d representing the time of two consecutive transmissions; Φ is based on the premise that the probability of the random variable d being greater than the maximum delay D is less than the probability of loss PL—the minimum transmission opportunity variable TX〇Pmin and the maximum transmission opportunity variable TXOPma) (look for an optimal transmission opportunity parameter τχορ. 3. Wireless area as described in claim 2 The network has a service quality guarantee method, and the above-mentioned "the probability that the random variable d is greater than the maximum delay D is less than the loss probability parameter PL, and the minimum transmission opportunity variable TXOPmin and the maximum transmission opportunity variable TXOpmax are sought. The step of an optimal transmission opportunity parameter TX〇p" includes the following steps: S-time calculation P(d>D) 'calculates the probability that the random variable d is greater than the maximum delay D(d>D);d>D) is greater than the loss probability parameter pL, if p(d>D) is greater than the loss probability parameter PL', the aforementioned maximum transmission opportunity parameter TX〇Pmax is equal to the value of the current transmission opportunity parameter TXOP, and returns to the aforementioned "minimum minimum The intermediate value of the transmission opportunity parameter TXOPmin to the maximum transmission opportunity parameter TXOPmax is taken as the current transmission opportunity parameter ΤχΟρ", otherwise the next step is performed; 201029386 determines whether the difference between P(d>D) and PL is small enough, ie Determine whether the difference between _p(d>D) and the loss probability parameter PL is less than a specific value of the bamboo raft. If it is less than the specific value, proceed to the next step. Otherwise, the minimum transmission opportunity parameter TXOPmin is equal to the value of the current transmission opportunity parameter τχ〇ρ, and returns to the aforementioned step of “taking the intermediate value of the minimum transmission opportunity parameter TX0Pmjn to the maximum transmission opportunity parameter TXOPmax as the current transmission opportunity parameter τχ〇ρ”. Depreciation, the transmission opportunity parameter of this 睥^f is * the most ',,, and transmission opportunity parameter TXOP when the collision probability parameter is P. Eight, the pattern: (such as the next page) ❹ 19