KR20040100537A - Method of offering multimedia service for wireless LAN - Google Patents

Abstract

PURPOSE: A method for providing a multimedia service in a wireless LAN(Local Area Network) system is provided to increase the throughput of data and decrease delay time by granting transmission priority to multimedia data in a wireless LAN system. CONSTITUTION: In case that a wireless terminal connected to a wireless LAN system attempts data transmission, but attempts the retransmission of the data due to a collision, the wireless LAN system judges whether the data that the wireless terminal wants to retransmit are multimedia data. If the retransmission data are multimedia data, the wireless LAN system multiplies the first backoff time by a specific number and sets the second backoff time. The wireless terminal transmits the multimedia data after the second backoff time.

Description

Method of providing multimedia service in wireless LAN system {Method of offering multimedia service for wireless LAN}

The present invention relates to a method for providing a multimedia service in a local area network (LAN) environment, and more particularly, to provide a quality of service (QoS) by giving priority to real-time services in a wireless LAN. The present invention relates to a method for providing a multimedia service of a system.

Recently, due to the universalization of the high-speed Internet network, the services used by most Internet users are also diversified from data-based to multimedia. With the advent of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless LAN, which supports mobility, which is the limitation of the existing wired LAN, more convenient data communication is possible and wireless at popular terminals such as PDA (Personal Digital Assistant), mobile phone, notebook, etc. As LANs are serviced, demand for wireless LANs is expanding.

The maximum transmission speed of IEEE 802.11b is 11Mbps (bit per second), but the actual speed is about 3 ~ 5Mbps. Considering that the speed of the high-speed Internet network is 1 ~ 4 Mbps, it seems easy to communicate with wireless LAN, but it is not enough to meet the evolution of multimedia services.

In order to satisfy real-time traffic QoS such as voice and video, protocols such as Resource reSerVation Protocol (RSVP) have been proposed on the Internet Protocol (IP) layer.

However, in order to apply the above protocol, in order to satisfy QoS requirements in the IP layer, it must be able to support such a protocol in the MAC (Media Access Control) layer.

The MAC protocol of IEEE 802.11 provides two basic access methods. It is a competition based protocol and a poll based protocol. Among them, the DCF (Distributed Coordination Function), a competition-based protocol, accesses a channel using a carrier sense multiple access with collision avoidance (CSMA / CA) method, which is efficient for best effort (BF) data transmission in a non-reserved manner.

In addition, the polling-based protocol PCF (Point Coordination Function) determines the turn to transmit in a polling method using an access point (AP) which is a point coordinator (PC). However, the PCF method has a disadvantage in throughput reduction due to the polling method. Therefore, both DCF and PCF methods are insufficient to transmit while satisfying QoS for real-time traffic.

In order to solve the above problems, the present invention is to modify the backoff algorithm of the DCF in a wireless LAN system to increase the throughput of traffic transmission of multimedia data, and to reduce the delay time of the wireless LAN system of the The purpose is to provide a multimedia service providing method.

1 illustrates a method of operating a DCF in a MAC of the IEEE 802.11 standard.

FIG. 2 is a diagram illustrating CW increased according to the number of collisions in the IEEE 802.11 standard.

3 is a graph comparing multimedia data transmission probabilities between a method of providing a multimedia service of a wireless LAN system and a method using a related art according to an exemplary embodiment of the present invention.

4 is a diagram simulating VoIP traffic delay time for the number of terminals according to an embodiment of the present invention.

5 is a diagram illustrating a data throughput for the number of terminals according to an embodiment of the present invention.

6 is a view simulating the VoIP traffic collision rate for the number of terminals according to an embodiment of the present invention.

According to another aspect of the present invention, there is provided a method for providing a multimedia service of a wireless LAN system.

In a method of providing a multimedia data service of a wireless LAN system in which a plurality of wireless terminals connected to a wireless LAN system attempts to transmit data and attempts to retransmit when a collision occurs, the first wireless terminal tries to retransmit data. Is multimedia data, and when the data to be retransmitted by the second radio terminal is general data instead of multimedia data, the second radio terminal applies the backoff time applied by the first radio terminal for retransmission for retransmission. By setting the time shorter than the backoff time, the priority is given to the multimedia data retransmission so that the multimedia data can be retransmitted first.

Method for providing a multimedia service of a wireless LAN system according to another aspect of the present invention,

A method of providing a multimedia data service of a wireless LAN system in which a wireless terminal connected to a wireless LAN system attempts to transmit data and attempts to retransmit when a collision occurs, the method comprising: (a) data to be retransmitted by the wireless terminal; Determining whether is multimedia data; (b) if the data retransmitted by the wireless terminal is multimedia data as a result of the determination, setting a second backoff time by multiplying a first backoff time set by a backoff adjustment scheme with a specific number; And (c) the terminal transmitting multimedia data after the newly set second backoff time.

The method may further include transmitting multimedia data after the first backoff time when the data to be retransmitted by the wireless terminal is not multimedia data.

The first backoff time may be calculated by the following equation.

2nd backoff time = [2 ^{i + 1} × random ()] × slot time

Here, 'i' is the number of retransmissions of retransmission of data, and slot time is a basic slot time required for data transmission.

In this case, the specific number is greater than '0' and less than '1'.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

1 illustrates a method of operating a DCF in a MAC of the IEEE 802.11 standard.

Referring to FIG. 1, DCF, which is a basic access method of the MAC of the IEEE 802.11 standard, checks a channel whether another terminal is transmitting before transmitting. If the channel is detected to be empty for a longer time interval than the DIFS (DCF Interframe Space), the terminal transmits a packet. In this case, the DIFS is an interval of DCF which is an interval between frames used when the WLAN medium is available. When the terminal attempts to access, the DIFS is an interval to wait until the medium is not in use.

That is, assuming that terminal A, terminal C, and terminal D transmit data to terminal B, first, terminal A transmits data (①) to terminal B, and terminal B responds to the reception of data (①). Transmit to terminal A.

The terminal C and the terminal D wait for a fixed fixed time, and random delay time. , Wait for each, and then try to transfer each data.

At this time, In this case, since the terminal C starts to send data (②) first, the data (③) sent by the terminal D collides with the data transmitted from the terminal C, and thus the terminal D cannot transmit the data (③).

In order for the terminal D to send data ③, the terminal D must wait for a random backoff time and attempt transmission.

At this time, the backoff process is started to determine the time to wait, and the backoff time calculation is as follows.

Backoff time = [2 ^{i + 1} × random ()] × slot time, i = i th transmission

The contention window (CW) increased according to the number of collisions generated when the terminal D transmits data is changed. CW is a value related to the backoff count of the terminal and the backoff counter is set to a pseudorandom value between 0 and CW.

FIG. 2 is a diagram illustrating CW increased according to the number of collisions in the IEEE 802.11 standard.

2, it can be seen that the value of CW increases proportionally as the number of times of retransmission due to collision occurs.

Therefore, in case of multimedia data such as voice over IP (VoIP), video, audio, etc., where real-time transmission is important, real-time transmission is not guaranteed.

To this end, the present invention can modify the backoff algorithm shown in Equation 1 to give priority to the multimedia data, thereby increasing the probability of transmitting multimedia data in which real time transmission is important by reducing the waiting time.

That is, the backoff time calculation algorithm is modified as follows, and the backoff time according to Equation 2 is calculated.

if (non multimedia traffic) --------------- (1)

Then mode = 1

else --------------- (2)

Then mode = β

Backoff time = [2 ^{i + 1} × random ()] × slot time × mode, where i is the i th transmission

According to Equation 2 above, if a random variable called mode is introduced for prioritization, and Equation 1, in which the same backoff time is applied to all data traffics, is modified, it is not multimedia traffic (non multimedia traffic). (1) allows the conventional backoff time to be applied (mode = 1), otherwise (2), i.e. for multimedia traffic, the value of 'β' is less than '1' and '0'. It is set to be larger so as to multiply the backoff time calculation formula, resulting in an effect of reducing the actual backoff time as shown in Equation 2 above.

Therefore, the multimedia data is given a priority because the backoff time is set smaller than that of the general data. Comparing the transmission probability of the multimedia data with respect to the case of applying the equation (2) and the case of applying the equation (1) is as follows.

3 is a graph comparing multimedia data transmission probabilities between a method of providing a multimedia service of a wireless LAN system and a method using a related art according to an exemplary embodiment of the present invention.

Referring to FIG. 3, in the transmission time slot, the transmission probability is represented by the standard 200, and the probability is represented by the backoff algorithm of Equation 1, and the high probability 100 is represented by the embodiment of the present invention. The probability for the case of applying the modified backoff algorithm as shown in Equation 2 according to Equation 2 is given.

As shown in FIG. 3, it can be seen that multimedia data is transmitted with high probability when Equation 2 according to an embodiment of the present invention is applied.

FIG. 4 is a diagram simulating VoIP traffic delay time for the number of terminals according to an embodiment of the present invention, FIG. 5 is a diagram simulating data throughput for the number of terminals according to an embodiment of the present invention, and FIG. A simulation of the VoIP traffic collision rate for the number of terminals according to an embodiment of the present invention.

4 to 6, the case of applying the back off time according to Equation 1 represented by the solid line (−) and setting the mode (= β) value to 0.1 ( ) And the mode value set to 0.5 ( ), And the mode value is set to 0.9 ( ) Was compared and simulated.

Referring to FIG. 4, as a result of simulating time delay according to the number of terminals transmitting VoIP data, when the mode value is 0.1, when the number of terminals transmitting the VoIP data is 65, the mode value is 0.5 or 0.9. It can be seen that the time delay increases sharply since about 75 terminals transmit VoIP data.

In addition, referring to FIG. 5, it can be seen that the data throughput is lowered when the algorithm according to the embodiment of the present invention has about 60 to 70 or more terminals, and thus the throughput increases.

Referring to FIG. 6, it can be seen that the VoIP data collision rate shows a difference according to the mode value and is significantly lower than the original IEEE802.11 collision rate.

In addition, as a simulation result according to an embodiment of the present invention, a mode value of about 0.5 to 0.9 was found to be the most efficient value.

As described above, the method for providing a multimedia service of a wireless LAN system according to the present invention has the effect of increasing the throughput of multimedia data and reducing the delay time by assigning the priority of transmission of the multimedia data in the wireless LAN system. .

Claims (5)

In a method of providing a multimedia data service of a wireless LAN system in which a plurality of wireless terminals connected to a wireless LAN system attempts to transmit data and attempts to retransmit data when a collision occurs, If the data to be retransmitted by the first wireless terminal is multimedia data and the data to be retransmitted by the second wireless terminal is general data instead of multimedia data, the first wireless terminal applies the backoff time applied for retransmission. 2. The method of providing a multimedia data service of a wireless LAN system, wherein the wireless terminal sets a shorter time than a backoff time applied for retransmission, so that the priority of the multimedia data is retransmitted so that the multimedia data can be retransmitted first. In a method of providing a multimedia data service of a wireless LAN system in which a wireless terminal connected to a wireless LAN system attempts to transmit data and attempts to retransmit data when a collision occurs, (a) determining whether the data to be retransmitted by the wireless terminal is multimedia data; (b) if the data retransmitted by the wireless terminal is multimedia data as a result of the determination, setting a second backoff time by multiplying a first backoff time set by a backoff adjustment scheme with a specific number; And (c) the terminal transmitting multimedia data after the newly set second backoff time Multimedia service providing method of a wireless LAN system comprising a. The method of claim 2, And transmitting the multimedia data after the first backoff time when the data to be retransmitted by the wireless terminal is not multimedia data as a result of the determination of step (a). . The method of claim 2 or 3, The first backoff time is calculated by the following equation, the multimedia service providing method of a wireless LAN system. 1st backoff time = [2 ^{i + 1} × random ()] × slot time Here, 'i' is the number of retransmissions of retransmission of data, and slot time is a basic slot time required for data transmission. The method of claim 1, And the specific number is greater than '0' and less than '1'.