KR20060024268A - Method and device of a priority-based medium access control by using distributed polling to support quality of service in ad-hoc networks - Google Patents

Abstract

The present invention discloses a method and apparatus for priority-based distributed polling method for guaranteeing quality of service in an ad hoc network. In order to transmit the current frame, the UE transmits an RTS frame. In this RTS frame, the UE transmits a next frame to be transmitted using the priority information of other stations. UEs in the same area can know whether the right of the next frame transmission is their own through this RTS frame. Therefore, the priority-based distributed polling method in the ad hoc network can reduce the possibility of collision that can occur in a single medium and ensure the quality of service (QoS) according to the priority.

Ad-hoc networks, Quality of Service (QoS), Medium Access Control (MAC), Distributed polling

Description

Method and device of a priority-based medium access control by using distributed polling to support quality of service in ad-hoc networks             

1 is a diagram illustrating a media access method according to the prior art, respectively.

2 is a diagram illustrating a signaling procedure of CSMA / CA which is a method basically used in an ad hoc network.

3 is a diagram illustrating a backoff process that is switched when a collision occurs due to contention competition between terminals.

FIG. 4 is a diagram illustrating a modification of an RTS frame defined by the existing IEEE 802.11 proposed in the present invention to support distributed polling according to the priority of each UE frame. FIG.

FIG. 5 is a diagram illustrating a method of expressing that a user is present in a network by generating a pulse after a PIFS time when a polled terminal does not have a frame to transmit.

6 is a view showing the operation of the priority-based distributed polling method according to the present invention.

7 is a flowchart of a priority based distributed polling method proposed in the present invention.

8 is a schematic structural diagram of an apparatus for supporting a priority based distributed polling method according to the present invention;

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

710: Temporary Frame Storage 711: MAC Address Table

721: Priority information table storage 722: Priority next terminal selector

723: pulse generator 730: MAC controller

740: media sensing device 750: media contention module

760: frame control information generator 770: timer

780: backoff timer 790: frame analyzer

900: general wireless mobile terminal module 910: antenna module

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for priority-based distributed polling media access control that guarantees quality of service (QoS) in ad-hoc networks, particularly in an ad hoc network using a single medium. Priority-based distributed polling scheme to reduce collisions caused by contention of each terminal for use and to ensure quality of service (QoS) of ad hoc network through efficient and reliable transmission of frames The present invention relates to a method and apparatus for newly designed medium access control.

In general, ad hoc networks (Ad-hoc Networks) is studying the standardization of protocols for mobile ad hoc networks in the IETF Mobile Ad hoc Network (IETF MANET) working group, a network composed of groups of mobile terminals, that is, a fixed base ( It is a network that enables mobile terminals to cooperatively communicate with each other without infrastructure, and includes IEEE 802.11 Wireless LAN (WLAN), IEEE 802.15 Wireless Personal Area Network (WPAN), Home Area Network (HAN), Used in the communication field, Ad hoc MAC protocol and Ac hoc routing protocol are being studied to support MANET at LLC (Logical Link Control) and MAC (Medium Access Control) levels of the data link layer.

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

Ad-hoc networks: networks that allow mobile terminals to communicate cooperatively without a fixed infrastructure

Station: A device that independently transmits and receives a frame with a wireless communication device (notebook, PDA, etc.)

AP (Access Point), PC (Point Coordinator), HC (Hybrid coordinator): Device that relays and controls the communication of terminals within the relay range with a single radio range

Contention: In an environment defined as a single medium, each terminal in the same area undergoes a contention process for frame transmission.

Collision: When a plurality of UEs attempt frame transmission simultaneously on a single medium, collision occurs and transmission fails due to a frame error.

Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA): In order to prevent collisions in the wireless medium, when a request is sent to the RTS frame and a clear to send frame is received before attempting to transmit the frame, It is a signaling procedure methodology that transmits an actual frame and an acknowledgment (ACK) frame when the complete transmission of the frame is successfully completed.

Contention Window (CW): Each UE has a contention window divided into fixed time slots. Through this, each terminal can reduce the probability of collision and achieve sequential transmission of frames. However, if 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 a large size of its contention window. This is called a backoff process.

Polling: The right to send a frame. Polling allows you to send a frame only when your order is returned.

IFS (Interframe Space): When transmitting a frame, each real frame and control frame need to be transmitted and received. There are three types of time intervals between each frame: SIFS, PIFS, and DIFS. In the case of IEEE 802.11e, DIFS is converted to AIFS.

SIFS (Short Interframe Space): The shortest waiting time interval. Used between RTS, CTS, DATA, and ACK (Acknowledgment).

PIFS (Point Interframe Space): It is larger than SIFS and shorter than DIFS. To use PCF or HCF, it is controlled by AP (Access Point).

DIFS (Distributed Interframe Space): Longer than PIFS. If the transmission of the frame is successfully completed, it waits for DIFS time before entering the race and attempts to transmit the frame.

AIFS (Arbitrary Interframe Space): You can adjust the waiting time for the first attempt to secure the media according to the priority of the frames. AIFS is equal to or greater than DIFS. The frame with the highest priority is equal to the smallest AIFS, or DIFS. The smaller the priority, the larger the AIFS.

Ad-hoc network (Ad-hoc Network) refers to a communication network that can communicate with each other within a certain protocol, the terminal equipped with each wireless communication device, unlike the existing base station-oriented wireless communication. This network eliminates the need for basic infrastructure, enabling the construction of active and flexible communications networks. There are many kinds of protocols for communication of each terminal of the ad hoc network, but the most widely introduced protocols are wireless LAN protocols.

In general, a wireless LAN refers to an IEEE 802.11 standard standardized by the Institute of Electrical and Electronics Engineers (IEEE). This specification defines two parts, which are divided into the part defining actual radio resource and the method for accessing the radio resource. Infrared and radio frequency are defined as a wireless medium for accessing a terminal, and dual radio frequencies are widely used. In addition, a medium access control (MAC) method is defined as a transmission protocol through a wireless medium. There are two methods, a distributed coordination function (DCF) mode and a point coordination function (PCF) mode. These two methods do not provide quality of service (QoS) because they use the same parameters and approach.

To solve this problem, IEEE is defining a standard called IEEE 802.11e, which is a modification of the existing IEEE 802.11 that can provide differentiated services according to the class of frames in the existing IEEE 802.11 WLAN standard. IEEE 802.11e defines the Enhanced Distributed Coordination Function (EDCF) mode and the Hybrid Point Coordination Function (HCF) mode by substituting DCF mode and PCF mode, which are two medium access control (MAC) methods of IEEE 802.11e. .

DCF mode and EDCF mode are methods for acquiring the right of frame transmission through contention. In PCF mode and HCF mode, the central coordinator is located in each radio area to determine the transmission order of each terminal to relay communication through polling. It's a way of control. Thus, in the DCF mode and the EDCF mode, frame collision may occur due to contention of terminals, but collision does not occur in PCF and HCF. However, the important issue is that it is not suitable for ad hoc networks because PCF mode and HCF mode require a basic infrastructure called central coordinator (AP).

With many of the currently introduced methods, we are trying to achieve better quality of service by using or modifying DCF mode or EDCF mode for ad hoc networks. However, since DCF mode and EDCF mode attempt to transmit frames based on contention, collisions increase due to limited contention window as frame load increases, and there is a problem in that performance and efficiency of communication network are drastically decreased. As a solution to this problem, the PCF mode or the HCF mode method, which uses media by using polling to order the frame transmission rather than the contention based contention, is useful. It may not be available on the network.

The basic medium access control (MAC) protocol of IEEE 802.11 is as follows. First, each terminal constantly monitors the state of the wireless medium. If another terminal is using the medium, even if there is a frame to be transmitted, the terminal waits without attempting to transmit the frame. If there is a frame to be transmitted and the wireless medium is not in use, the UE attempts to transmit the frame after DIFS time. In order to transmit the frame, the UE randomly sets the size of the contention window (CW) and decreases by one slot each time each frame transmission is confirmed. Eventually, if its contention window becomes 0 (1 in IEEE 802.11e), the frame is immediately transmitted. If a collision is detected at this time, the contention window is increased by randomly selecting the contention window and then reducing the time slot. .

1. Detailed Signaling Procedure for Frame Transmission in Conventional Wireless LAN Protocol

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 the terminals causing the collision will be penalized to select a larger CW than before. The size of the contention window (CW) starts at the minimum defined by the standard (CWmin), and doubles up to a predefined maximum value (CWmax) at each point in time when there is an increase in the load on the medium. If the RTS frame is successfully transmitted, other frames are sequentially separated and transmitted at intervals of a short inerframe space (SIFS).

FIG. 3 shows a backoff method used in contention-based media access control when a collision occurs due to contention contention at each terminal.

Referring to FIG. 3, 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 is large, but the access delay is long. In order to solve the 'hidden node problem' and 'exposed node problem' and to determine the state of the medium, IEEE 802.11 provides a physical carrier sense mechanism and a virtual carrier sense mechanism. Function (virtual carrier sense function) is used. Physical carrier sense mechanisms are provided at the physical layer, but virtual carrier detection mechanisms are provided at the CSMA / CA, i.e., frame link layer, based on Multiple Access with Collision Avoidance for Wireless Networks (MACAW).

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 designate a polling list of a PC, the terminal must go through a joining process with the PC.

As described above, the DCF mode does not require the basic infrastructure of the network, and is suitable for the ad hoc environment because the 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

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 of the system increases. In order to reduce collisions, UEs having frames to transmit increase CW twice by CWmax whenever transmission fails. As CW increases, the probability of collision decreases, but with a longer delay time. In the EDCF mode, the collision occurrence probability is greater than in the case of DCF, because 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 EDCF mode uses a virtual collision avoidance method, this is only a method for reducing the collision inside each terminal, the collision of the terminals will increase than the existing DCF mode.

  In high load situations, PCF and HCF 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 at high loads, but there is a problem that it cannot be used in an ad hoc network due to the installation problem of the central coordinator.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to add a priority information field of each terminal of an ad hoc network to each RTS frame, and to select a next terminal according to the priority of the terminal. Add a field to transmit the polling information to determine the priority by applying priority-based distributed polling method to CSMA / CA in DCF mode or EDCF mode, which is basically used in ad hoc networks. It is a priority-based distributed polling scheme that guarantees the quality of service in ad hoc networks that provide reliable quality of service (QoS) by dramatically reducing the occurrence of collisions in the network environment and providing different differentiated services to the priority of frames. It is to provide a medium access control method.

Another object of the present invention is to provide a priority-based distributed polling media access control apparatus which guarantees the quality of service in an ad hoc network which is particularly suitable for implementing the apparatus.

In order to achieve the object of the present invention, the present invention provides a priority-based medium access control (MAC) method for guaranteeing quality of service (QoS) in ad-hoc networks, Detecting a changed RTS frame in a structure that guarantees quality of service (QoS) by supporting distributed polling according to the priority of each terminal frame of another terminal and confirming whether the terminal exists in its priority information table; If the transmission address of the detected RTS frame does not exist in its priority information table, adding it to the priority information table of its own terminal; Confirming whether a terminal having a next transmission opportunity in the detected RTS frame is itself; Waiting for the next RTS frame to be detected if the UE having the next transmission opportunity in the detected RTS frame is not itself; Checking whether there is a frame to be transmitted in its temporary frame store when the UE having the next transmission opportunity in the detected RTS frame is its own; If the terminal having the next transmission opportunity through the RTS frame is its own, after the signaling procedure of the current terminal is over, it checks whether the medium is IDLE and waits if not IDLE. If the medium is IDLE, its priority is set after PIFS time. Determining a terminal to be selected next using the information table and transmitting its own RTS frame including the terminal to be selected next; Calculating a terminal having a next transmission opportunity in the RTS frame (Equations 1, 2a, and 2b); Displaying a terminal having a next transmission opportunity in an RTS frame; When the UE having the next transmission opportunity through the RTS frame is its own, when there is no frame to transmit, all terminals generate a pulse indicating that there is no data to be transmitted after the PIFS time after the current UE's signal procedure ends. Indicating to sense a pulse; Executing, by the UE selected according to the priority, a signaling procedure leading to RTS, CTS, DATA, and ACK for frame transmission; The other terminals receiving the pulse are switched to the backoff / competition mode after the DIFS time; And a step in which the selected terminal immediately switches to the backoff / competition mode due to the waiting time in the signaling procedure leading to the RTS, the CTS, the DATA, and the ACK for the frame transmission (Ad-hoc). Networks) provides a priority-based distributed polling method of media access control that guarantees quality of service (QoS).

In order to achieve the above object of the present invention, the present invention provides a priority-based medium access control (MAC) device for guaranteeing quality of service (QoS) in Ad-hoc Networks, A temporary frame storage 710 for temporarily storing a frame to be transmitted by the terminal; A frame analyzer 790 for analyzing the destination of the frame and the nature of the frame currently stored in the temporary frame storage 710; A MAC address table 711 for storing the MAC address of the mobile terminal in the ad hoc network; A frame control information generator 760 designed to create various control frames and control connections according to a medium access control method for guaranteeing quality of service (QoS) by supporting each frame with priority-based distributed polling in the ad hoc network; A priority information processing module 720 for processing polling information according to priority information of a mobile terminal in the ad hoc network; A media contention module 750 for switching back to contention mode and managing a backoff and a collision window when a collision occurs; A timer 770 for managing and generating each IFS (Inter Frame Space) and time information; A backoff timer 780 for managing a backoff process of attempting to reduce the probability of collision by setting the size of a contention window (CW) of the terminal to a large size when a collision occurs; A MAC controller 730 that oversees the overall media access control process; Provided is a priority-based media access control apparatus for guaranteeing the quality of service in an ad hoc network, characterized in that the media sensing device 740 for detecting the use of the medium.

According to the present invention, the RTS / CTS exchange mechanism solves the problem of hidden nodes, and it is possible to reduce the impact of the collision by making it known that the collision occurs in a relatively short RTS frame rather than a longer data frame. In the present invention, the priority information field of each terminal of the ad hoc network is added to each RTS frame in each RTS frame, and a field for transmitting polling information for determining the next terminal according to the priority of the terminal is added. When the UE selected according to the priority has a frame to transmit, the UE transmits an RTS frame after PIFS (Point Inter Frame Space) time so that the UE has a unique right of using a wireless medium. The PIFS time is shorter than the DIFS time when the unselected terminals do not send an RTS frame to prevent collision. If the selected UE does not have a frame to transmit, it transmits a 'no-RTS' pulse between the PIFS time and the DIFS time. In this case, all other UEs may access the DCF or EDCF channel using the existing contention method after the DIFS time. .

The priority-based distributed polling method of media access control for guaranteeing quality of service (QoS) in an ad hoc network newly proposed by the present invention provides the following methods.

1. Modified structure of RTS frame transmitted when attempting to access media for frame transmission

2. Table of priority information which each UE has in order to provide polling information according to priority

3. How to Maintain Information in the Priority Information Table

4. How to determine the terminal to be selected next

5. Method for notifying when the selected terminal does not have a frame to transmit

6. Signaling procedure for frame transmission and reception

7. How to switch in case of collision

In the present invention, in order to designate a terminal having a priority of frame transmission when a mobile terminal in an ad hoc network transmits an RTS frame, the following matters are considered after the frame transmission of the corresponding terminal is finished.

1) Each terminal of the ad hoc network should have a priority information table including priority information of all terminals.

2) There is a need for a method of generating polling information for providing QoS to various priority terminals.

3) The priority information table should be updated whenever the configuration of the ad hoc network changes. For example, when a new terminal enters a network cluster or when an existing terminal suddenly loses power at a specific time, it may be considered.

The present invention uses the following method to solve the above-mentioned problems of the prior art.

1) In order to know the priority of each terminal in the ad hoc network, each terminal adds a priority information field when transmitting the RTS frame. Also, in order to give another UE a right to transmit a frame, a field for transmitting polling information is added to the RTS frame.

4 shows an RTS frame defined in the existing IEEE and an RTS frame 310 modified in the method proposed in the present invention. The next-polled address (NA) field 311 added to the existing RTS frame is the address of the terminal to be selected next, and the PRI (priority) field 312 is the priority of the transmitting terminal. Each terminal of the ad hoc network records the MAC address and priority information of another terminal of the RTS frame in its priority information table.

 2) Each terminal has a station priority table including MAC addresses and priorities of all terminals in the ad hoc network. In the present invention, PRI has a value of 1 or more. The terminal transmitting the RTS frame selects the terminal having the next transmission right in the RTS frame and adds the MAC address of the selected terminal to the NA field. First, the current terminal transmitting the RTS to select the terminal to be selected generates a random number R that satisfies the following equation (1).

 N is the number of terminals in the network area, PRIn is the priority value of the n-th terminal. The current terminal transmitting the RTS frame selects the terminal k that satisfies Equation 2. When the number of terminals in the reception range of the terminal increases or decreases, the terminal of the terminal changes according to the sum of priorities of all terminals.

3) After the PIFS time, if there is no RTS frame from the terminal selected by polling, it is necessary to distinguish whether the selected terminal has no frame to transmit or whether it is already out of the ad hoc network (actually out of network or sudden power loss). There is. In order to distinguish between these two situations, the present invention uses a pulse as shown in FIG. A pulse is an energy pulse that does not need to have a frame structure. FIG. 5 is a diagram illustrating a method of expressing that a user is present in a network by generating a pulse after a PIFS time when a terminal polled according to priority does not have a frame to transmit.

As shown in FIG. 5, if the selected UE does not have a frame to transmit, it should generate a pulse before the DIFS time to inform other UEs that its UE is still in the ad hoc network. The other terminals maintain the information of the terminal in their own table and maintain the opportunity to select the terminal next time. If the other terminals do not detect the pulse, each terminal determines that the terminal is not in the ad hoc network and deletes the information of the terminal after a short interval from their table.

4) When a new mobile terminal is added to the ad hoc network, all terminals must know the arbitrary MAC address and priority information of the added terminal. The new terminal detects the medium and waits for a competition opportunity to send an RTS frame. When the terminal existing in the ad hoc network detects the RTS frame, the terminal first checks whether the sender's MAC address exists in its priority information table. If the sender's MAC address does not exist in its priority information table, add the sender's MAC address and priority to its priority information table. If the terminal leaves the ad hoc network, the other terminals will delete the information of the terminal from the table and will not select any more. If the next terminal polled according to the priority has a frame to be transmitted, the RTS frame is transmitted after the PIFS time after the frame transmission of the current terminal is completed. Polled UEs have absolute priority because other non-polled UEs transmit RTS at DIFS time following PIFS.

6 shows the operation of the priority-based distributed polling method according to the present invention. When UE 1 in an ad hoc network transmits an RTS frame, it selects a next UE that has a right to transmit an RTS frame in preference to other UEs in the next data transmission time according to the priorities of the UEs. Polling information is included in the RTS frame. After receiving the RTS frame, the other terminals check the polling information to find out whether they have been selected by the received RTS frame. If one of the terminals is selected and the selected terminal (terminal 4) has a frame transmitted in its queue, the terminal 4 sets a network allocation vector (NAV) and prioritizes the terminal to be selected in the next RTS to be transmitted. Calculate using a table. The UE 4 waits for the PIFS time after the end of the current frame transmission and reception, and immediately transmits the RTS frame without performing a backoff process. If it does not have a frame to transmit to transmit the pulse of Figure 5 to inform other terminals of its existence. If the selected terminal (terminal 4) informs that it will not transmit a frame by sending a pulse, other unselected terminals use a contention method of the existing DCF mode or EDCF mode as a method for securing a medium.

7 is a flowchart of a priority based distributed polling method proposed in the present invention.

In a priority-based medium access control (MAC) method for guaranteeing quality of service (QoS) in ad-hoc networks,

Supports distributed polling according to the priority of each terminal frame of another terminal in the medium, and detects the changed RTS frame 310 to guarantee the quality of service (QoS) and checks whether the terminal exists in its priority information table. (Steps S1-S3).

If the detected transmission address of the RTS frame 310 does not exist in its own priority information table, it is added to its own terminal to the priority information table (step S4).

In step S5, the terminal having the next transmission opportunity in the detected RTS frame is identified as its own. If the terminal having the next transmission opportunity in the detected RTS frame is not itself, the next RTS frame may be detected. To wait (step S6).

If the terminal having the next transmission opportunity in the detected RTS frame is itself, it is checked whether a frame to be transmitted exists in its temporary frame storage 710 (step S7).

If the terminal having the next transmission opportunity through the RTS frame is its own, after the signal procedure of the current terminal is finished, it is checked whether the medium is IDLE (step S8). If not, it waits (step S9). After waiting for PIFS time (step S10), a terminal to be selected next is determined using its own priority information table (step S11), and then its own RTS frame is transmitted including the terminal to be selected (step 12). Wait for the CTS frame. If the CTS received waiting time is less than the preset timeout, the DATA frame is transmitted (step S15) and the ACK is waited (step S16). If the ACK received waiting time is less than the preset timeout, the medium detection step ( Returning to the process S1), if the waiting time received is equal to or greater than the preset timeout time, the process proceeds to the RTS, CTS, DATA, ACK, which is switched to the backoff / competition section (step S17).

After transmitting the RTS frame (S12), the terminal having the next transmission opportunity is calculated in the RTS frame (see Equation 1, 2a, 2b) and the terminal having the next transmission opportunity is displayed in the RTS frame.

If there is no frame to transmit in step S7 (waiting until the current medium = IDLE) (steps S18-S19), if the terminal having the next transmission opportunity through the RTS frame is itself, when there is no frame to transmit After waiting for the PIFS time after the terminal signal processing (step S20), a pulse indicating that there is no data to be transmitted is generated (step S21) and all terminals are detected to sense the pulse (step S22).

Thereafter, the UE selected according to the priority performs a signal procedure leading to RTS, CTS, DATA, ACK for frame transmission; The CTS received waiting time or the ACK received waiting time exceeding a preset waiting time (Timeout), or other terminals receiving a pulse are switched to the backoff / competition mode after the DIFS time (step S23); And

The selected terminal executes a signaling procedure leading to RTS, CTS, DATA, and ACK for frame transmission (steps S24-S29), and immediately switches to the backoff / competition mode when the waiting time is exceeded.

Referring to FIG. 8, a medium access control (Medium Access Control) for supporting a priority-based distributed polling method for guaranteeing quality of service (QoS) in ad-hoc networks according to the present invention; MAC) apparatus includes a temporary frame storage 710 for temporarily storing a frame to be transmitted from each terminal; A frame analyzer 790 for analyzing the destination of the frame and the nature of the frame currently stored in the temporary frame storage 710; A MAC address table 711 for storing the MAC address of the mobile terminal in the ad hoc network; A frame control information generator 760 designed to create various control frames and control connections according to a medium access control method for guaranteeing quality of service (QoS) by supporting each frame with priority-based distributed polling in the ad hoc network; Priority information table storage 721 for storing the priority information of each terminal when receiving the RTS frame of each terminal to know the priority of the terminal, and the priority information table storage ( 721 and a next priority terminal selector 722 having a function of selecting a terminal to be selected next to be included in its RTS frame by the terminal connected with the transmission opportunity, and the terminal receiving the transmission opportunity has no frame to transmit. A priority information processing module 720 for processing priority information of the mobile terminal in the ad-hoc network, including a pulse generator 723 for indicating this after a PIFS time; A media contention module 750 for switching back to contention mode and managing a backoff and a collision window when a collision occurs; A timer 770 for managing and generating each IFS (Inter Frame Space) and time information; A backoff timer 780 for managing a backoff process of attempting to reduce the probability of collision by setting the size of a contention window (CW) of the terminal to a large size when a collision occurs; A MAC controller 730 that oversees the overall media access control process; And a medium sensing device 740 for sensing the use of the medium.

The present invention can reduce the probability of collision between terminals using a priority-based distributed polling method even in an ad hoc environment and increases channel utilization compared to IEEE 802.11 and 802.11e. In traditional DCF and EDCF modes, as the overall rate increases, the number of collisions increases gradually until the overall rate reaches the channel rate. On the other hand, in the present invention, as the load increases, polling can be made more successfully because the UEs selected according to the priority have frames to transmit in their queues. In DCF mode and EDCF mode, collision increases as UEs increase, and in EDCF mode, collisions increase more rapidly due to limited contention window size (CW) for UEs with higher priority. In the present invention, the collision may increase as the number of terminals increases, but increases significantly compared to the DCF mode and the EDCF mode. The terminal selected in the present invention may transmit an RTS frame after a shorter waiting time (PIFS) than when compared with IEEE 802.11 (DIFS + backoff time) or IEEE 802.11e (AIFS [TC] + backoff time).

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 priority-based media access control method and apparatus for guaranteeing the Quality of Service (QoS) in Ad-hoc Networks according to the present invention are added to the RTS frame defined in IEEE. By adding a priority information field of each terminal of the network and a field for transmitting polling information for determining the next terminal according to the priority of the terminal, each terminal for using the medium in an ad hoc network using a single medium. In order to reduce contention conflicts and to ensure quality of service (QoS) through efficient and reliable transmission of frames, QoS can be supported and high throughput can be achieved by using a new priority-based distributed polling scheme. .

The present invention reduces the number of collisions in the Medium Access Control (MAC) layer and supports high throughput and differentiated QoS. In addition, the strict support of bandwidth allocation according to various priorities in the ad hoc network, it is effective to apply various types of priorities.

Claims (12)

In a priority-based medium access control (MAC) method for guaranteeing quality of service (QoS) in ad-hoc networks, Detecting a changed RTS frame in a structure that guarantees quality of service (QoS) by supporting distributed polling according to the priority of each terminal frame of another terminal in the medium and confirming whether the terminal exists in its priority information table; If the transmission address of the detected RTS frame does not exist in its priority information table, adding it to the priority information table of its own terminal; Confirming whether a terminal having a next transmission opportunity in the detected RTS frame is itself; Waiting for the next RTS frame to be detected if the UE having the next transmission opportunity in the detected RTS frame is not itself; Checking whether there is a frame to be transmitted in its temporary frame store when the UE having the next transmission opportunity in the detected RTS frame is its own; If the terminal having the next transmission opportunity through the RTS frame is its own, after the signaling procedure of the current terminal is over, it checks whether the medium is IDLE and waits if not IDLE. If the medium is IDLE, its priority is set after PIFS time. Determining a terminal to be selected next using the information table and transmitting its own RTS frame including the terminal to be selected next; Calculating a terminal having a next transmission opportunity in the RTS frame (Equation 1, 2a, 2b); Displaying a terminal having a next transmission opportunity in the RTS frame; When the UE having the next transmission opportunity through the RTS frame is its own, when there is no frame to transmit, all terminals generate a pulse indicating that there is no data to be transmitted after the PIFS time after the current UE's signal procedure ends. Indicating to sense a pulse; Executing, by the UE selected according to the priority, a signaling procedure leading to RTS, CTS, DATA, and ACK for frame transmission; The other terminals receiving the pulse are switched to the backoff / competition mode after the DIFS time; And Ad-hoc networks, characterized in that the selected terminal includes the step of switching to the back off / competition mode immediately due to the waiting time in the signaling procedure leading to RTS, CTS, DATA, ACK for frame transmission Priority-based distributed polling method for ensuring quality of service (QoS). The method of claim 1, In the ad hoc network, all mobile terminals have a priority priority table which each terminal has in order to provide polling information according to priority. When the new terminal is added to the ad hoc network, adding the sender's MAC address and priority to each mobile terminal's own MAC address and priority information to the priority information table; And When the mobile terminal leaves the ad hoc network, the other terminals further include deleting the MAC address and priority information of the terminal, respectively, from the priority information table. Rank-based distributed polling method of media access control. The method of claim 1, The Request to Send (RTS) frame changed to a structure that guarantees quality of service (QoS) by supporting distributed polling according to the priority of each UE frame is a field of an RTS frame defined in the existing IEEE 802.11 (Frame Control, Duration, RA). , TA, FCS) A Next-polled Address (NA) field indicating an address of a terminal to be selected next; And Priority guaranteeing quality of service (QoS) in Ad-hoc Networks, characterized by using a distributed polling method by adding a PRI (priority) field indicating the priority of the transmitting terminal. Rank-based distributed polling method of media access control. The method of claim 1, The modified RTS frame structure indicates a terminal to transmit the next frame by using priority information of other stations that it owns, so that terminals within the same region are entitled to the next frame transmission through the changed RTS frame. Priority-based guarantees of quality of service in an ad hoc network, which can be realized and, in this way, can reduce the possibility of collisions that can occur in a single medium and ensure quality of service (QoS) according to priority. Distributed polling method of media access control. The method of claim 1, In the ad hoc network, CDMA / CA, which is a basic method of the DCF mode or the EDCF mode, which is basically used to reduce the possibility of a collision which may occur in a single medium between mobile terminals and guarantees the quality of service (QoS) according to the priority. A priority-based distributed polling method of media access control that guarantees quality of service in an ad hoc network, characterized by using a priority-based distributed polling scheme. The method of claim 2, In the ad hoc network After the PIFS time, if there is no RTS frame from the terminal selected by polling, it is necessary to have a frame structure to distinguish between two situations, whether the selected terminal has no frame to transmit or has already left the ad hoc network according to the priority. If the polled UE does not have a frame to transmit, it generates a pulse after PIFS time to indicate that its UE exists in the ad hoc network. If not, the pulse should be generated before the DIFS time to inform other terminals that they are still in the network. The other terminals maintain the information of the terminal in their priority information table, and maintain the opportunity to select the terminal next time,  If the other terminals do not detect the pulse, each terminal 'determines that the terminal is not in the network and deletes the information of the terminal after a predetermined interval in their priority information table in the ad hoc network Priority-based distributed polling method of media access control to guarantee quality of service. The method of claim 4, wherein When a new mobile terminal is added to the ad hoc network, all terminals wait for a competitive opportunity to detect a medium and send an RTS frame in order to know any MAC address and priority information of the added terminal. When the existing terminal detects the RTS frame, the terminal first checks whether the sender's MAC address exists in its priority information table, and if the sender's MAC address does not exist in its priority information table, the sender Adding the MAC address and priority to its own priority information table; If the terminal leaves the ad hoc network, the other terminals will delete the information of the terminal from the table and no longer select it; If the next terminal to be polled has a frame to transmit, transmitting a RTS frame after PIFS time after the frame transmission of the current terminal is completed; And Since the other unpolled terminals transmit the RTS frame at DIFS time following the PIFS, the polled terminal further includes the step of transmitting the frame with absolute priority, thereby ensuring the quality of service in the ad hoc network. Rank-based distributed polling method of media access control. The method of claim 1, Operation of the priority-based distributed polling method When the terminal 1 transmits the RTS frame, it selects the next terminal having the right to transmit the RTS frame in preference to the other terminals in the next data transmission time according to the priorities of the terminals, polling information is included in the RTS frame, other terminals After receiving the RTS frame, they check the polling information to see if they have been selected by the received RTS frame, If one of the terminals is selected and the selected terminal (terminal 4) has a frame transmitted in its queue, the terminal 4 sets a network allocation vector (NAV) and prioritizes the terminal to be selected in the next RTS to be transmitted. Is calculated using a ranking table, UE 4 waits for the PIFS time after the transmission and reception of the current frame, and immediately transmits an RTS frame without performing a backoff process. If it does not have a frame to transmit and transmits the pulse to inform other terminals of their existence, If the selected UE (terminal 4) informs that it will not transmit a frame by sending a pulse, other UEs not selected use the contention method of the existing DCF mode or EDCF mode as a method for securing a medium. Priority-based distributed polling method of media access control to guarantee service quality in ad hoc networks. The method of claim 1, In the ad hoc network, collisions increase as UEs increase in DCF mode and EDCF mode. In EDCF mode, collisions increase more rapidly due to limited contention window size (CW) for UEs with higher priority, and collisions increase in UE number. It can be increased as it increases, but when the collision occurs by the media contention module, it switches to the competition mode to manage the backoff and the collision window. By setting, the terminal selected according to the priority by using a backoff timer that manages the backoff process that attempts to reduce the probability of collision is either IEEE 802.11 (DIFS + Backoff Time) or IEEE 802.11e (AIFS [TC] +). Ad hoc network, which transmits an RTS frame after a shorter waiting time (PIFS) than compared to How the media access control priorities based distributed polling scheme to ensure quality of service. In a priority-based medium access control (MAC) device that guarantees Quality of Service (QoS) in Ad-hoc Networks, A temporary frame storage 710 temporarily storing a frame to be transmitted from each terminal; A frame analyzer 790 for analyzing the destination of the frame and the nature of the frame currently stored in the temporary frame storage 710; A MAC address table 711 for storing the MAC address of the mobile terminal in the ad hoc network; A frame control information generator 760 designed to create various control frames and control connections according to a medium access control method for guaranteeing quality of service (QoS) by supporting each frame with priority-based distributed polling in the ad hoc network; A priority information processing module 720 for processing polling information according to priority information of a mobile terminal in the ad hoc network; A media contention module 750 for switching back to contention mode and managing a backoff and a collision window when a collision occurs; A timer 770 for managing and generating each IFS (Inter Frame Space) and time information; A backoff timer 780 for managing a backoff process of attempting to reduce the probability of collision by setting the size of a contention window (CW) of the terminal to a large size when a collision occurs; A MAC controller 730 that oversees the overall media access control process; Priority-based distributed polling method of the media access control device for guaranteeing the quality of service in the ad hoc network, characterized in that consisting of a medium detection device for detecting the use of the medium (740). The method of claim 10, The priority information processing module 720 A priority information table storage 721 for storing priority information of each terminal when receiving an RTS frame of each terminal to know the priority of the terminal; A priority next terminal selector 722 connected to the priority information table storage 721 and having a function of selecting a terminal to be selected next to be included in its RTS frame by the terminal receiving the transmission opportunity; And Priority-based distributed polling media access control device for guaranteeing the quality of service in an ad hoc network, characterized in that it comprises a pulse generator 723 for indicating after the PIFS time when the terminal receiving the transmission has no frame to transmit . The method of claim 10, All mobile terminals in the ad hoc network In order to provide polling information according to priority, each terminal has a priority priority table, which has a priority information table, and the priority information table includes an increase in the number of mobile terminals whose configuration in the ad hoc network changes. When decreasing, i.e. when a new terminal is added to the ad hoc network, the MAC address and priority of the sender are added to each mobile terminal's own MAC address and priority information to the priority information table, and the mobile terminal is ad hoc. Priority-based distributed polling media access guaranteeing the quality of service in an ad hoc network, characterized in that when leaving the network, other terminals delete the information (MAC address and priority information) of the leaving terminal from the priority information table. controller.

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