KR100620124B1 - Method and device of load-based dynamic backoff algorithm to support quality of service in contention-based shared medium - Google Patents

Abstract

The present invention relates to a backoff method and apparatus in a media access control apparatus based on contention in a single shared medium. In a content-based media access control method, if a collision occurs due to contention, a backoff procedure is entered. The present invention proposes a method for efficiently and adaptively performing a backoff procedure using two parameters that can be calculated in real time during a medium access control process. The basic idea is to measure the state of the medium in the short and long term and use it in the backoff process. This reduces the number of conflicts and ensures quality of service based on priorities.

Medium Access Control (MAC), Backoff Algorithm, Quality of Service (QoS), Contention-based Wireless Shared Medium

Description

Method and device of load-based dynamic backoff algorithm to support quality of service in contention-based shared medium}             

FIG. 1 is a diagram illustrating communication of frames of priority by mapping each priority frame to four separate queues.

2 is an attempt to communicate after having different access wait times by priority.

3 is a diagram illustrating a backoff process that operates for a media acquisition competition of each terminal.

4 is a diagram illustrating CSMA / CA, which is a method of completing one frame transmission by transmitting and receiving an RTS-CTS-DATA-ACK for efficient frame transmission and reception.

FIG. 5 illustrates the concept of an LMS predictor used to predict an expected collision rate operating as a long term media determinant in the present invention. FIG.

6 is a diagram illustrating a method of calculating slot utilization, which acts as a short term medium determining factor in the present invention.

7 shows a corresponding graph for mapping media determination coefficients according to priorities in the present invention.

8 is a flowchart illustrating a backoff method proposed in the present invention.

9 is a schematic structural diagram of an apparatus for supporting a load-based dynamic backoff method according to the present invention;

<Explanation of symbols for the main parts of the drawings>

810: Temporary Frame Storage 820: MAC Address Table

830: frame analyzer 840: frame control information generator

850: Timer 860: Media Competition Module

870: backoff timer 880: medium status determination module

881: long term medium determinant calculator 882: short term medium determinant calculator

883: Media Determination Coefficient Calculator 910: MAC Rule Controller

920: media sensing device 930: general wireless mobile terminal module

940: antenna module

The present invention relates to a method and apparatus for dynamic media access control backoff for effectively handling a collision when guaranteeing a quality of service in a device performing communication using a wireless single medium. In particular, in a wireless single competition medium designed to reduce the collision caused by the competition of each terminal to use the medium in a communication device using a single medium, and to guarantee quality of service (QoS) through efficient and reliable frame transmission. A method and apparatus for load-based dynamic media access control backoff to guarantee the quality of service of a service.

In general, a representative standard using a wireless single shared medium may be a standard of the IEEE 802.11 WLAN series, a wireless LAN standard proposed by the IEEE. This standard defines a series of methods for communication between terminals using the ISM unlicensed band. The physical layer (PHY), which defines the characteristics and standards of the media, and the data link layer, which defines the method of transmitting and receiving frames. That's Medium Access Control. The IEEE 802.11 Working Group is currently defining a new standard called IEEE 802.11e to ensure quality of service (QoS) in the existing IEEE 802.11 family of standards. In the case of IEEE 802.11e, the physical layer is not defined, but the method in the media access control layer is newly defined.

First, the main terms defined in this description and their meanings are defined as follows.

Station: A device capable of independently transmitting and receiving a frame with a wireless communication device (a laptop, a PDA, a handset having a wireless LAN module, etc.)

Contention: In an environment defined as a single medium, each UE within the same propagation range is subject to contention for frame transmission.

Collision: When a plurality of UEs attempt to transmit a frame at the same time in a single medium at the same time, a collision occurs. At this time, transmission fails due to a frame collision error.

Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA): Sends a request to send (RTS) frame smaller than the data frame before attempting to transmit the frame in order to prevent collisions in a single wireless medium. The process of transmitting the actual data frame when receiving a clear to send (CTS) frame from the computer. The receiving terminal side receiving the data frame is completed by transmitting an acknowledgment (ACK) frame to the transmitting terminal side.

Contention Window (CW): Each terminal has a contention window divided into time slots defined by fixed times. Through this, each terminal can reduce the probability of collision and achieve sequential frame transmission. However, when each terminal selects the same contention window value, a collision occurs.

Backoff Procedure: When a collision occurs, the terminal attempts to reduce the probability of collision by setting the size of its contention window to be large. This is called a backoff process.

IFS (Interframe Space): When transmitting a frame, each frame and control frame need to be transmitted and received. There are SIFS, DIFS, and AIFS that define an extra time interval between each frame.

SIFS (Short Interframe Space): The shortest waiting time interval. The RTS frame, the CTS frame, the data frame, and the ACK frame always wait for the SIFS time interval.

DIFS (Distributed Interframe Space): It is longer than SIFS time interval. The other terminals, which have sensed that the transmission of the frame has been successfully completed, enter into a race after waiting for DIFS time interval before entering the race to secure a medium.

Arbitrary Interframce Space (AIFS): In the case of IEEE 802.11e for QoS support, the waiting time for first attempting to secure a medium can be adjusted according to the priority of the medium. AIFS latency is equal to or longer than DIFS latency. The frame with the highest priority is equal to the smallest AIFS latency, or DIFS latency, and the lower the priority, the larger the AIFS latency.

AC (Access Cartegory): A set of priorities defined to indicate the adjustment factors according to priorities.

As described above, a general wireless LAN is an IEEE 802.11 standard defined by the Institute of Electrical and Electronics Engineers (IEEE). This specification defines two parts, which are divided into a part that defines actual radio resources (PHY) and a part that defines a method for accessing radio resources (MAC). Infrared and radio frequency are defined as a wireless medium for accessing a terminal, and radio frequencies are widely used.

IEEE 802.11 uses Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) as a medium access method, and central control by a distributed coordination function (DCF) and a base station (base station) PCF (Point Coordination Function) is used. In addition, to solve the hidden node problem and the exposed node problem, the Request To Send (RTS) / Clear To Send (CTS) exchange can be selectively used.

IEEE 802.11 is developing a standard that is developed to meet various needs of users. In particular, IEEE 802.11e is an extension of IEEE 802.11 as a standard for providing QoS. A feature of IEEE 802.11e is that differentiation of access frame (interframe space) according to each priority and differentiation of contention window size during the backoff period operating in the event of a collision. This enables differentiated services based on priorities.

IEEE 802.11e, which is currently being standardized, defines HCF (Hybrid Coordination Function) to provide QoS based on priority. HCF adds two methods for contention period (CP), which is a contention period, and contention free period (CFP), which is a contention-free period, which includes the EDCA used by CP and HCF Controlled Channel Access (HCCA) used by CFP. will be. In addition, in order to support QoS according to UP (User Priority) based on IEEE 802.1D, IEEE 802.11e provides four ACs. Each AC defines AIFS [AC] (Arbitration Interframe Space) which is differentiated according to priority level, competition windows CWmin [AC], CWmax [AC], and TXOP [AC] (Transmission Oppportunity) which is authority of transmission time. In addition, QoS support is provided through a series of parameters. In the case of EDCA, the media is secured through competition, and if a collision occurs, a backoff procedure is performed. In the case of HCCA, a hybrid coordinator (HC) located in a QBS (QoS Basic Service Set) uses polling to control transmission and reception of frames.

DCF mode and EDCA mode is a method of acquiring the right of frame transmission through competition, and PCF mode and HCCA mode relay the communication by polling by determining the transmission rank of each terminal with the central coordinator located in each radio area. And control. Thus, in the DCF mode and the EDCA mode, frame collision may occur due to contention of UEs, but collision does not occur in PCF mode and HCCA mode. However, the important issue is that the PCF and HCF modes are not suitable for ad hoc networks because they require a basic infrastructure because they are central coordinators (APs).

FIG. 1 shows a method of mapping eight UP (User Priority) of IEEE 802.1D to four priority multi-queues defined in IEEE 802.11e.

In EDCA, the higher the priority frame, the shorter the access wait time for transmission. Also, the higher the priority, the smaller the size of the competing windows CWmin [AC] and CWmax [AC], and consequently, frame transmission can be attempted after using a relatively small time slot.

2 shows the use of different AIFS [AC] wait times for each priority.

1. Detailed Signaling Procedure for Frame Transmission in Existing Wireless LAN Standards

When there is a frame to transmit in each queue, each station enters a medium for frame transmission. In order to detect the use of media, IEEE 802.11 uses two media sensing techniques, one is the physical carrier sense mechanism at the physical layer (PHY), and the other is a virtual sensing function called virtual. It is a virtual carrier sense mechanism. If the UE detects that the medium is idle, each UE waits for AIFS [AC] time, which is a waiting time according to each priority, and then randomly determines a time slot in the currently set competition window so that the time slot is 0. Decrease time slot until During the reduction process, if the use of the medium is detected by the terminal's attempt to transmit the time slot to 0, the operation stops immediately and waits until the use of the medium is finished. The usage time of the medium is provided through a network allocation vector (NAV) included in a header frame. When the size of the time slot becomes zero, each terminal immediately transmits a frame (data frame or RTS frame). At this time, if there is another terminal that has reached zero at the same time, a collision occurs. In the case of IEEE 802.11e, unlike IEEE 802.11, since the queue consists of four independent multiple queues for each priority, the virtual scheduler for preventing collisions in each queue for each terminal is managed by the queue.

1 and 2 illustrate a method of CSMA / CA as a signaling procedure for securing a medium in ad hoc networks. In CSMA / CA, when a terminal detects that the medium is idle for a DIFS time, the MS decreases the backoff counter and attempts to transmit a frame when the backoff time reaches zero. The backoff counter is randomly selected in the contention window CW. The collision may occur when the same backoff time is selected in a plurality of terminals. When a collision occurs, the terminals increase their CW range and randomly select a new CW to repeat the new backoff process. This means that terminals causing the collision will be disadvantaged to select a larger contention window (CW) than before. The size of the contention window (CW) starts with the minimum defined in the standard (CWmin), and doubles up to a predefined maximum value (CWmax) at each time the load on the medium increases and a collision occurs. If the RTS frame is successfully transmitted, other frames are sequentially separated and transmitted at intervals of a short inerframe space (SIFS).

3 shows an operation procedure of CSMA / CA. Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) achieves one complete frame transmission through an exchange procedure of RTS, CTS, DATA, and ACK.

FIG. 4 illustrates a backoff method used in contention-based media access control when collision occurs due to contention contention at each terminal.

Referring to FIG. 4, a mutual change between a large CW and a small CW is illustrated. As the size of the competitive window (CW) increases, the probability of collision can be reduced, so that the resolution ability increases, but the access delay is long.

PCF mode is based on the polling method of a central coordinator called a point coordinator (PC). During the contention-free period of the PCF mode, the PC terminal designates a polling list. In order to specify the polling list of the PC, the terminal must go through a combined process with the PC.

As described above, the DCF mode does not require the basic infrastructure of the network, and is suitable for an ad hoc environment because terminals can communicate with each other. On the other hand, PCF mode based on infrastructure is inadequate for ad hoc environment, but can provide limited QoS, and can increase channel utilization when system load increases.

2. Problems of Existing WiFi Standards

Although IEEE 802.11e improves existing methods to enable differentiated services of frames according to priorities in the competitive mode, the performance decreases rapidly as the number of terminals in the QBSS increases or the load increases. It is showing. In order to solve this problem, the HCCA mode is defined to increase the utilization of media by using polling through the central controller HC. However, this can be used in a fixed place where the network configuration can limit the mobility of the terminal. Can be. Therefore, in the case of HCCA mode, it is not suitable for Ad-hoc Networks that communicate through a variable network configuration, and since the adjustment by the central controller is not possible, the performance improvement of the EDCA mode through competition is more important than anything else. It is important.

However, the Binary Exponential Backoff algorithm (BEB) method, which is a backoff algorithm used in the contention period, has a 'fairness problem'. In particular, as the load of the medium increases, the collision of the medium between terminals increases rapidly. There is a problem that the medium utilization rate is significantly reduced. This problem occurs because the BEB method fixedly defines and uses a contention window. The BEB method refers to a method of attempting to transmit a frame by doubling the current contention window each time a collision occurs and returning to the minimum contention window when the transmission is successful.

As described above, the IEEE 802.11 DCF mode does not support desired QoS for each terminal. This is because all terminals use the same parameter value and the same media access method. In the DCF mode, many collisions occur at the same time, and the utilization rate of the channel decreases as the load on the system increases. In order to reduce collisions, UEs having frames to transmit increase the contention window (CW) by 2 times to CWmax whenever transmission fails. If the contention window CW increases, the probability of collision decreases, but it has a longer delay time. In the EDCA mode, the collision occurrence probability is greater than in the case of DCF, since a smaller CW is assigned to UEs or frame types having a higher priority than others. As the load on the system increases-especially when higher priority frames increase-the number of collisions increases rapidly and the utilization of the channel decreases rapidly as terminals with relatively small CWs compete to access the medium. It becomes the cause. Although the EDCA mode uses a virtual collision avoidance method, this is only a method for reducing the collision inside each terminal, the collision of the terminals is increased than the existing DCF mode.

In high load situations, PCF and HCCA modes, which use polling methods to avoid collisions, increase throughput, and reduce latency, can be used to improve performance. However, the polling method can improve performance under high loads, but there is a problem that it cannot be used in ad hoc networks due to the installation problem of the central coordinator.

The present invention has been proposed to solve the backoff problem of the prior art, and an object of the present invention is to change the existing system frame structure in a communication system that uses the existing wireless single shared medium and follows the CSMA / CA access procedure. Collision probability by dynamically adjusting the size of the contention window (CW) according to the load of the network to change the time slot-based backoff method to reduce collisions in the communication network and increase the probability of successful frame transmission. To provide a method and apparatus for a load-based dynamic media control backoff to ensure the quality of service in a single radio contention medium that reduces the network efficiency, and efficiently provides quality of service (QoS) to increase the utilization of the network.

In order to achieve the above object of the present invention, the present invention provides a medium access control backoff method for guaranteeing a quality of service (QoS) of a communication system using a wireless single shared medium. A first step of calculating an expected collision rate of a next cycle by determining a collision rate for each update cycle by determining whether the long-term medium determination factor for the size change is updated; A second step of determining whether an update period of a short-term medium determining factor for changing a size of a contention window is calculated and calculating a utilization rate of a time slot for each update period; A third step of calculating a medium determination coefficient by using long-term and short-term medium determination factors obtained from the expected collision rate and the time slot utilization determined for each update period; A fourth step of determining the media determination coefficient for each priority by using the calculated media determination coefficient; And a fifth step of calculating a contention window size for the case where the frame transmission succeeds or the frame transmission fails by using the determined medium determination coefficient.
In order to achieve the above object of the present invention, the present invention provides a load-based dynamic medium access control backoff apparatus for guaranteeing the quality of service in a wireless single content medium, as a long-term medium determination factor for contention window determination in frame transmission A long-term medium determinant calculator for calculating the expected collision rate; A short term medium decision factor calculator for calculating a utilization rate of a time slot provided as a short term medium decision factor for determining a contention window; And a medium determination coefficient calculator for determining a medium determination coefficient for the contention window determination through the long term and short term medium determination factors.

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Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following examples are only for exemplifying the present invention, and the content of the present invention is not limited to the following examples.

The present invention relates to a method and apparatus for backoff in a medium access control (MAC) device based on contention in a single shared medium. In the contention-based medium access control (MAC) method, when a collision occurs due to contention, a backoff procedure is entered. The present invention proposes a method for efficiently and adaptively performing a backoff procedure by using two parameters that can be calculated in real time during a medium access control (MAC) process. The basic idea is to measure the state of the medium in the short and long term and use the backoff procedure to reduce the number of collisions and to ensure quality of service (QoS) according to priorities.

An efficient backoff method is to define how to handle the current contention window (CW) when frame transmission succeeds and fails. The backoff methodology is important because it can increase the usability of the media without changing the basic structure. In addition, it is difficult to control the network through a central controller such as HC in an active and variable network such as ad hoc networks. Since the UEs in the ad hoc network must communicate autonomously through the competition to secure the media, it is important to find an efficient backoff method to increase the competition-based communication performance when using a single shared medium.

In order to increase the utilization of the medium, the proposed method to monitor the state of the medium in the short and long term and actively apply it to the increase and decrease of the competitive window is as follows. The basic approach of the present invention is to define two parameters that can be easily identified in the media access control operation of each terminal and use them to update the size of the immediate contention window (CW) according to the state of the media. To this end, the present invention uses an expected collision rate that occurs during a frame transmission attempt of each terminal as a long-term medium determining factor, and uses a backoff (short-term medium determining factor). Backoff) is used to determine the size of the contention window (CW) by using the slot utilization of the time slot.

1. Long-term Medium Determinants (LDF)

First, the collision rate is defined using the number of frame transmission attempts attempted by the terminal, and used as a long-term medium decision factor (LDF). The collision rate is defined as the number of transmission attempts and the number of collisions during a certain period j in each terminal p. As shown in Equation 1, the collision rate for a certain period of time j can be easily calculated by the number of transmission of the RTS frame that attempts to transmit a frame to be transmitted in the queue of each UE and the number of ACK frames received when the frame transmission is successful. have. The number of retransmission attempts of the RTS frame is not continuous but is limited by defining a limit of the number of retransmission attempts. The long-term medium determinant is calculated as in Equation 1.

는 고정된 값으로 충돌율의 변화에 능동적으로 반응할 수 있도록 하기 위해 사용된다.The current collision rate, which is determined every time in a period j time slot, is not sufficient to determine the size of the contention window in a future (j + 1) interval. Therefore, in the present invention, the collision rate in the next long period (j + 1) period is calculated using a Least Mean Square (LMS) predictor and used as an expected collision rate LDF for determining the size of the contention window. FIG. 5 illustrates the operation of a Least Mean Square (LMS) predictor used to predict an expected collision rate operating as a long-term medium determinant in the present invention. The basic operating procedure of the LMS is shown in equations (2) and (3). The expected collision rate (k = 1) of the next period is calculated using the actual collision rates of the previous long sections. Wn is a time varying coefficient vector for minimizing an error occurring in the difference between the predicted value and the actual value. The LMS predictor can accurately predict the congestion state change of the current network on a scale of long interval time, thereby enabling media access control adaptive to the network environment. The amount of data frames in the QBSS actually used is variable, and thus the network load varies according to time, so it can be seen that it can be actively applied to the backoff method. Of equation (3)

Is a fixed value that can be used to actively respond to changes in the collision rate.

2. Short-term Media Determinants (SDF)

The second element defined in the proposed invention is the utilization of time slots using the value of the contention window (CW), which attempts to transmit one frame in each terminal, which is a short-term decision factor (SDF). Use as. It is readily appreciated that the utilization of time slots can determine the state of the medium. When there is a frame to be transmitted in the queue of each terminal, each terminal needs to go through a backoff procedure for the frame transmission, so the size of the time slot used for frame transmission and the time waited by other terminals It is possible to infer the media load degree through the number of slot time points. 6 illustrates a backoff of each terminal and a slot usage situation associated with it. First, when the use of the medium is detected due to a transmission attempt of a specific terminal in which the time slot reaches 0, terminals operating different backoff procedures stop reducing the time slot and indicate that the time slot at that time is used. The slot utilization is calculated using the total number of backoff time slots set by the user and the number of time slots used by other terminals during a predetermined period i. When calculating the slot utilization, it is not considered whether the transmission of the frame was successful or a collision occurred at the time when the medium was used, and when the use of the medium is detected, the time slot at that time is used.

The slot utilization rate through the time slot used during the time during the predetermined period i is expressed by the following equation (4).

단기 매체 결정 인자 SDF의 갱신 주기 i는 장기 매체 결정 인자 LDF의 갱신 주기 j보다 현저히 작으며, LDF와 SDF는 한 단말내의 서로 다른 우선순위의 트래픽에 공통적으로 적용된다. LDF와 SDF의 조합을 통해 최종적으로 매체의 상태를 결정하는 매체 결정 계수 D_medium[AC]를 결정한다. LDF와 SDF의 값의 범위는 [0, 1] 까지 이다.

The update period i of the short term medium determinant SDF is significantly smaller than the update period j of the long term medium determinant LDF, and LDF and SDF are commonly applied to traffic of different priorities in one terminal. The combination of LDF and SDF determines the medium determination coefficient D _medium [AC] which finally determines the state of the medium. The range of values for LDF and SDF is up to [0, 1].

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3. Medium determination coefficient (D _medium [AC])

When the LDF and the SDF are calculated using the expected collision rate and the slot utilization rate, the medium determination coefficient D _medium [AC] is finally calculated to define the contention window (CW). D _medium [AC] in the present invention is defined as follows.

값은 LDF와 SDF사이의 값의 비중을 결정하기 위한 값이며, 이를 통해 각 우선 순위별 D_medium[AC] 값을 결정하게 된다. 각 AC에 따라 다른 D_medium[AC] 값을 사용함으로써 우선순위에 다른 차별화된 서비스를 가능하게 한다. 도 7은 D_medium[AC]의 반응 곡선을 보여준다.In Equation 5, LDF means the predicted collision rate of the next long term predicted by using the previous collision rate in the long term j to which the i th short segment belongs, and SDF means U ⁱ _slot measured in the i th short term. . AC_level is a value defined for each AC and is defined as 0, 1, 2, and 3 for each weighted high priority. 0 has the highest priority, and 3 has the lowest priority.

The value is used to determine the specific gravity of the value between the LDF and the SDF, through which the D _medium [AC] value for each priority is determined. The use of different D _medium [AC] values for each AC enables different differentiated services in priority. 7 shows the response curve of D _medium [AC].

4. Determination method of proposed competitive window (CW)

The size of the contention window CW is determined as follows using the determined D _medium [AC] value.

1) When frame transmission is successful

The Weight value is a weight commonly applied to determine an effective competition window.

2) When frame transmission fails

When frame transmission fails, a scale vector V _scale [AC] is defined to change a contention window, and V _scale [AC] is expressed by using Equation 9 from V [AC] obtained from Equation 8 [0.9, 1.1].

Along with the calculated V _scale [AC], the PF [AC] values for each priority are used together.

Finally, when frame transmission fails, Equation 10 is used to change the size of the contention window.

PF [AC] (Persistence Factor) is a predetermined fixed value for each priority. The use of PF [AC] is used to effectively change the discriminatory competitive window according to priority.

The reason for limiting the value of D _medium [AC] used for successful transmission to 1 is to prevent the contention window of a terminal that has successfully transmitted a frame from becoming larger than the contention window currently set, even if the medium is not good. . In addition, even if the frame transmission fails, it is possible to change the value according to the medium state through the present and past values of the D _medium [AC] value.

8 is a flowchart illustrating a backoff method proposed in the present invention.

8 shows a flowchart of the method proposed in the present invention. In addition to the CSMA / CA method, which is a medium access method, the factor value is periodically updated for each long and short period and applied to the backoff method. Each parameter value can be easily obtained in the procedure for transmitting a frame.

First, each terminal determines whether there is a frame to transmit [S1], and if there is a frame to transmit, it detects the use of the medium according to the CSMA / CA methodology [S3]. If the medium is not in use, it waits as much as AIFS [AC] corresponding to the frame priority [S4], and if the medium is not in use [S5], the time slot is randomly determined in its current competition window [S6]. If the use of the medium is detected during the process of reducing the time slot [S7], the decrease of the time slot is stopped [S8] and the process is waited until the medium is not used [S20]. When the time slot reaches 0 while reducing the time slot [S9], the frame is transmitted while transmitting and receiving the RTS, CTS, DATA, and ACK frames according to the CSMA / CA procedure [S10]. If the timer is operated during this process and the transmission / reception waiting time of each frame exceeds a predetermined time, it is considered that a collision has occurred [S11, S12, S13]. If a collision occurs during the transmission process and transmission of the frame fails, the contention window size is changed. At this time, the long and short period factor values for determining the next contention window are updated. [S14, S15, S16, S17, S22, S23, S24, S25]. The medium determination coefficient is calculated through the updated factor value [S18, S26]. Finally, the contention window is reset [S19, S27].

9 is a schematic structural diagram of an apparatus for supporting a load-based dynamic backoff method according to the present invention.

A load-based dynamic media access control backoff apparatus for guaranteeing quality of service (QoS) in a wireless single contention medium according to the present invention includes a temporary frame storage 810 for temporarily storing a frame to be transmitted; A MAC address table 820 identifying a destination of a frame located within the temporary frame store; A frame analyzer 830 for identifying the characteristics of the frame; A frame control information generator 840 for adding information necessary for transmission of the frame; A timer 850 for providing time according to frame transmission; A media contention module 860 for providing rules for frame transmission through contention; A backoff timer 870 for providing time information during backoff operation; A media determination module 880 calculated for determining a contention window (CW); A MAC rule controller 910 which oversees the communication procedures; A medium sensing device 920 for detecting a state of use of a medium; A general wireless mobile terminal module 930 for performing actual communication; And an antenna module 940 for communication.

Also, the medium determination module 880 includes a long term medium determination factor calculator 881 that calculates an expected collision included in the medium determination module and provided as a long term medium determination factor; A short term medium decision factor calculator 882 that calculates a utilization rate of a time slot provided as a short term medium decision factor; And a medium determination coefficient calculator 883 which determines the final medium determination coefficient through the long and short medium determination factors.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art various modifications of the present invention without departing from the spirit and scope of the invention described in the claims below. Or it may be modified.

As described above, the load-based dynamic media access control backoff method and apparatus for guaranteeing the Quality of Service (QoS) in a wireless single contention medium according to the present invention operate when a media collision occurs. The newly defined off operation can be expected to reduce the collision of the medium and increase the utilization of the medium. As the medium determination coefficient changes according to the load condition of the network, the competitive window can be operated in a small range when the load is small, and the dynamic medium can be expected by operating a larger competitive window as the load becomes larger. It works.

The present invention reduces the number of collisions in the Medium Access Control (MAC) layer and supports high throughput and differentiated QoS. It can also adapt adaptively to sudden load changes in the network.

Claims (10)

A medium access control backoff method for guaranteeing a quality of service (QoS) of a communication system using a wireless single shared medium, A first step of calculating an expected collision rate of a next cycle by determining a collision rate for each update cycle by determining whether an update period of a long-term medium determination factor for changing a size of a contention window occurs when a collision occurs during frame transmission; A second step of determining whether an update period of a short-term medium determining factor for changing a size of a contention window is calculated and calculating a utilization rate of a time slot for each update period; A third step of calculating a medium determination coefficient by using long-term and short-term medium determination factors obtained from the expected collision rate and the time slot utilization determined for each update period; A fourth step of determining the media determination coefficient for each priority by using the calculated media determination coefficient; And A fifth step of calculating a contention window size when the frame transmission is successful or when the frame transmission fails by using the determined medium determination coefficient; A load-based dynamic medium access control backoff method as claimed in claim 1, characterized in that it comprises a. The method of claim 1, wherein the first process is Calculating a number of transmission attempts during a predetermined period; A second step of counting the number of times a collision occurred during a certain period; A third step of calculating a collision rate from the number of transmission attempts calculated in the first and second steps and the number of collisions during the update period of the long-term medium determination factor for changing the size of the contention window; And A fourth step of calculating an expected collision rate to be used during a next period using the calculated collision rate; A load-based dynamic media access control backoff method as claimed in claim 1, characterized in that it comprises a. 3. The method of claim 2, wherein the expected collision rate is calculated using a Least Mean Square (LMS) predictor. The method of claim 1, wherein the second process is Calculating a number of time slots in a contention window randomly set for frame transmission for a predetermined period; A second step of counting the number of times that the backoff process is stopped and waited when the use of the medium is detected due to a frame transmission attempt of the terminal in which the time slot of the contention window reaches 0 for a predetermined period; And A third step of calculating a utilization rate of a time slot using values calculated in the first and second steps during a short-term medium determination factor update period for changing the size of the contention window; A load-based dynamic media access control backoff method as claimed in claim 1, characterized in that it comprises a. The medium determination coefficient (D _medium [AC]) according to claim 1, wherein The long term medium determinant is called LDF, and the short term medium determinant is called SDF,

ego,

Is a value for determining the weight of the value between LDF and SDF, and AC_level is a value defined for each AC (Access Cartegory), and when it is defined as 0,1,2,3 for the highest priority,

A load based dynamic media access control backoff method as claimed in claim 1, wherein the quality of service in a wireless single race medium is calculated. The contention window size of claim 1, wherein the contention window is successful when the frame transmission is successful. The long term medium determinant is LDF, the short term medium determinant is SDF,

Is,

Is a value to determine the weight of the value between LDF and SDF, AC_level is a value defined for each AC (Access Cartegory), and is defined as 0,1,2,3 for the highest priority, and a Weight value is a weight. In this case, the media decision factor with priority

when,

A load based dynamic media access control backoff method as claimed in claim 1, wherein the quality of service in a wireless single race medium is calculated. The method of claim 1, wherein the contention window size when the frame transmission fails Scale vector Vscale [AC] to change the contention window.

And Vscale [AC] is

It is set to a value between V [AC] and [0.9, 1.1] obtained from (D _medium [AC]: medium determination coefficient for hypocriticality), and PF [AC] (Persistence Factor) is fixed in advance for each priority. Value,

A load-based dynamic medium access control backoff method as claimed in claim 1, characterized in that it is determined by. A load-based dynamic media access control backoff apparatus for guaranteeing a quality of service in a wireless single competitive medium, A long term medium determinant calculator for calculating an expected collision rate, which serves as a long term medium determinant for contention window determination in frame transmission; A short term medium decision factor calculator for calculating a utilization rate of a time slot provided as a short term medium decision factor for determining a contention window; And A media determination coefficient calculator for determining a media determination coefficient for the competition window determination through the long and short term media determination factors; A load-based dynamic medium access control backoff apparatus for guaranteeing a quality of service in a wireless single race medium, comprising: a medium determination module, comprising: a medium determination module; delete delete

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