KR20140034539A - Fairness enhancement scheme for multimedia traffic in ieee 802.11e wireless lans - Google Patents

Abstract

The present invention relates to a fairness enhancement method for multimedia traffic in a wireless LAN and, more specifically, to a fairness enhancement method for multimedia traffic in an IEEE 802.11e wireless LAN comprising: a first process for calculating transmission opportunity (TXOP) limit using channel utilization information of a network in a QoS access point (QAP); a second process for enabling the QAP to transmit the TXOP limit obtained in the first process to all terminals using a beacon frame; and a third process for calculating TXOP limit, which will be actually used, according to the queue utilization of the terminal and the TXOP limit which is obtained by the respective terminals by receiving the beacon frame. As above, a technical solution pursued in the present invention dynamically controls the TXOP limit value by considering the channel utilization and the queue utilization to solve a fairness problem according to a traffic amount in the IEEE 802.11e wireless LAN environment. When the channel usage rate of the whole networks is low, the large amount of the data packet is able to be transmitted according to the high rate of the unused channel rate. Channel competition rates are decreased by transmitting more data packets by allocating the larger TXOP limit to the terminal including many packets in the queue.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of improving fairness of multimedia traffic in a wireless LAN,

[0001] The present invention relates to a method for improving the fairness of multimedia traffic in an IEEE 802.11e wireless LAN, and more particularly, to a dynamic TXOP (Transmission Opportunity) control method considering a channel usage rate of a network and an amount of multimedia traffic of a terminal, And a method for improving the fairness of traffic.

Generally, the multimedia traffic should be transmitted to the receiving terminal within the delay bound. If the multimedia traffic is not transmitted to the receiving terminal within the delay limit, the traffic is discarded. This causes the quality of the multimedia traffic and the performance of the network to deteriorate.

IEEE 802.11e enhanced distributed channel access (EDCA) defines several parameters to provide service differentiation and quality of service (QoS) of traffic. A typical parameter is TXOP (Transmission Opportunity), and TXOP is time length and can transmit multiple data packets continuously for a given time.

In the current IEEE 802.11e standard, all terminals use the same TXOP value. All terminals operate smoothly if they transmit traffic generated in the same multimedia application. However, when a terminal transmits traffic generated in different multimedia applications, a fairness problem arises.

On the other hand, all terminals in the TXOP method of IEEE 802.11e EDCA have the same TXOP limit. When the amount of traffic of each terminal is the same, the bandwidth is allocated equally and no problem occurs.

However, if each terminal supports multimedia application services with different traffic generation rates, fairness problems arise. Because each traffic generation rate is different, each terminal has different amount of traffic.

In this situation, if all terminals use the same TXOP limit value, a terminal with a small amount of multimedia traffic can quickly transmit a data packet waiting in a queue. Therefore, the terminal satisfies the delay limit of the packet and has a good performance. However, a terminal with a large amount of multimedia traffic performs a number of backoff processes, which increases the waiting time for transmission of the packet.

As a result, the delay limit of the packet can not be satisfied and the receiving terminal discards the packet, thereby degrading the performance of the multimedia traffic. Therefore, terminals with low traffic volume always have better performance than many terminals. This causes a fairness problem between the terminals due to the amount of traffic.

1 is a diagram showing a standard deviation of the transmission success rate within the delay limit according to the number of terminals, delay delay transmission success ratio according to the number of terminals for the IEEE 802.11e EDCA method in which all terminals have the same TXOP limit Standard Deviation. Here, the delay limit transmission success rate indicates the ratio of the number of successfully completed packets satisfying the delay limit with respect to the total number of data packets transmitted to the receiving terminal.

As shown in FIG. 1, when the number of terminals is small, there is almost no difference in standard deviation. This is because the amount of traffic to be transmitted in the network is small and transmission is possible regardless of the amount of traffic of each terminal. However, if the number of terminals exceeds four, the standard deviation of transmission success rate for each terminal increases. This is because the packet transmission latency of a terminal having a large amount of multimedia traffic is increased and the transmission success rate is lowered.

In addition, when the number of terminals is six or more, the standard deviation becomes smaller because the transmission success rate of all terminals is lowered. As described above, there is a problem that QoS to be provided varies according to the amount of multimedia traffic for each terminal.

S. Kim, R. Huang, and Y. Fang. Deterministic priority channel access scheme for QoS support in IEEE 802.11e wireless LANs. IEEE Transactions on Vehicular Technology. Vol. 58, No. 2, (2009), 855-864. N. Cranley and M. Davis. An experimental investigation of IEEE 802.11e TXOP facility for real-time video streaming. Proceedings of IEEE Global Telecommunications Conference. (2007), 2075-2080. J. Zhu, A. Fapojuwo. A new call admission control method for providing desired throughput and delay performance in IEEE 802.11e wireless LANs, IEEE Transactions on Wireless Communications. Vol. 6, No. 2, (2007), 701-709. X. Chen, H. Zhai, and Y. Fang. Supporting QoS in IEEE 802.11e wireless LANs. IEEE Transactions on Wireless Communications. Vol. 5, No. 8, (2006), 2217-2227. S. Kim and Y.J. Cho. Channel time allocation scheme based on feedback information in IEEE 802.11e wireless LANs. Elsevier Computer Networks, Vol. 51, No. 10, (2007), 2771-2787.

SUMMARY OF THE INVENTION The present invention has been made in order to overcome the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for improving channel quality and channel utilization in an IEEE 802.11e wireless LAN environment by considering channel Utilization and Queue Utilization The present invention provides a method for improving the fairness of multimedia traffic in a wireless LAN that dynamically adjusts a TXOP limit value.

In addition, the present invention calculates the TXOP limit according to the channel utilization of the network in the QAP, and transmits through the beacon frame, and actually used according to the TXOP limit obtained after each terminal receives the beacon frame and the terminal's own queue utilization An object of the present invention is to provide a method for improving fairness of multimedia traffic in a wireless LAN including a process of calculating a TXOP limit.

The method for improving the fairness of multimedia traffic in the IEEE 802.11e WLAN according to the present invention for achieving the object of the present invention, in the method for improving fairness of multimedia traffic in the IEEE 802.11e WLAN, in QAP (QoS Accese Point) Calculating a Transmission Opportunity (TXOP) limit using Channel Utilization information of the network; QAP is a second step of transmitting the TXOP limit obtained in the first step to all the terminals through the beacon frame; And a third step of calculating a TXOP limit to be actually used according to the TXOP limit obtained by receiving each beacon frame and the UE's own queue utilization (Queue Utilization).

The method may further include measuring a channel use time during a beacon frame cycle time through carrier sensing in the QAP of the first process of the present invention, wherein the channel utilization factor divides a channel busy time by a beacon frame transmission period, [Equation 1] The busy time is a time when a channel is used regardless of the success or failure of transmission when each terminal transmits a packet.

[Equation 1]

Where C_Util is the channel usage rate, Busy is the channel busy time, and BeaconPeriod is the period of the beacon frame.

In the first step of the present invention, since the channel utilization rate fluctuates very irregularly every time the calculation is performed, if the calculated value is used as it is, the network performance is degraded. ]. ≪ / RTI >

&Quot; (2) "

Here, C_Util _current is the n-th beacon frame period calculated by measuring the channel utilization, C_Util _{n -1} n -1-th beacon frame is a moving average value calculation cycle after, C_Util _n is computed after moving the frame (n) th beacon period average And α is a smoothing factor, which is a value of [0, 1].

In the third step of the present invention, the queue utilization rate ( Q_Util ) is a value indicating how much data packets are stored in the queue, and is calculated using Equation (5).

&Quot; (5) "

Where Q _size is the maximum number of packets the queue can store, and Q _packet is the number of packets currently stored in the queue.

In the third process of the present invention, the queue usage rate is calculated using Equation (6) using a moving average window to reflect a traffic generation pattern.

&Quot; (6) "

Here, Q_Util _current queue is measured after the (n) th beacon frame received usage, Q_Util _{n -1} is the n -1-th beacon frame is received after the moving average value computation, Q_Util _n is the moving average value calculated after the n-th beacon frame received .

As described above, in order to solve the problem of fairness according to the amount of traffic in the IEEE 802.11e wireless LAN environment, the TXOP limit value is dynamically considered in consideration of channel utilization and queue utilization. If the overall network utilization is low, the ratio of unused channels is high to accommodate the transmission of more data packets.In this case, a larger TXOP limit is assigned to a terminal having many packets in the queue. Since many data packets can be transmitted, the channel contention rate is lowered.

In addition, the present invention can reduce the channel waste because the packet collision probability is lowered to improve the overall network performance, which reduces the QoS of multimedia traffic by using a relatively small TXOP limit to the terminal with a small number of data packets in the queue Although it may cause a problem, there is an effect that can provide a fair QoS regardless of the difference in the amount of traffic between all terminals.

FIG. 1 is a diagram showing a standard deviation of a transmission success rate within a delay limit according to a conventional number of terminals.
FIG. 2 is a diagram illustrating a channel usage rate change according to the number of terminals of the present invention.
FIG. 3 is a diagram illustrating a TXOP limit allocation process according to a channel usage rate in the QAP of the present invention.
4 is a diagram illustrating a change in a queue usage rate according to the number of terminals of the present invention.
5 is a diagram illustrating a process of assigning a TXOP limit according to a queue usage rate in a terminal of the present invention.
FIG. 6 is a diagram illustrating channel utilization rates and transmission success rate standard deviations according to the number of terminals of the present invention.
FIG. 7 is a diagram illustrating a queue usage rate and a standard deviation of transmission success rate according to the number of terminals of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating a TXOP limit allocation process according to a channel usage rate in the QAP of the present invention. FIG. 4 is a diagram illustrating a process of allocating a queue according to the number of terminals according to the present invention. FIG. 5 is a diagram illustrating a process of allocating a TXOP limit according to a queue usage rate in a terminal according to the present invention. FIG. 6 is a diagram illustrating a channel usage rate and a standard deviation of transmission success rate according to the number of terminals of the present invention, FIG. 7 is a diagram illustrating a queue usage rate and a standard deviation of transmission success rate according to the number of terminals of the present invention.

First, as shown in FIGS. 2 to 7, a method for improving fairness of multimedia traffic in a wireless LAN according to the present invention uses TXOP (Transmission Opportunity) by using channel utilization information of a network in a QAP (QoS Accese Point). ) first step of calculating the limit, QAP is a second step of transmitting the TXOP limit obtained in the first step to all the terminals through the beacon frame, and the TXOP limit obtained by each terminal receives the beacon frame and the UE's own queue And a third process of calculating the TXOP limit to be used according to the utilization rate (Queue Utilization).

The channel utilization information of the network is used to calculate the TXOP limit in the QAP (QoS Accese Point). Here, the channel usage rate is calculated by dividing the channel busy time by the beacon frame transmission period, and the busy time is a time when the channel is used regardless of whether the transmission is successful when each terminal transmits a packet.

QAP measures channel usage time during beacon frame cycle time through carrier sensing. If the measured channel busy time is Busy, the channel utilization rate ( C_Util ) is as follows.

[Equation 1]

Where BeaconPeriod represents the period of the beacon frame.

Since the channel usage rate calculated in Equation (1) fluctuates very irregularly every time the calculation is performed, the performance fluctuates greatly when the calculated value is used as it is. Therefore, it can not be used as it is in the TXOP limit calculation, so we use the moving average window as follows.

&Quot; (2) "

Here, is the _current C_Util and the channel use rate measured in the (n) th beacon frame period, C_Util _{n -1} is the moving average value calculation cycle after frame n -1 second beacon, C_Util _n is calculated after the cycle frame (n) th beacon It is the moving average value. α is a smoothing factor and has a value of [0, 1].

As shown in FIG. 2, the channel utilization rate increases as the number of terminals increases, assuming that one terminal does not use the entire channel, and the packet collision probability increases as the number of terminals increases. Therefore, retransmission of the packet occurs frequently and the channel usage rate increases.

Define four new parameters to compute TXOP _QAP . The upper limit ( C_Util _high ) and the lower limit ( C_Util _low ) of the channel usage rate are defined as the TXOP limit maximum value ( TXOP _QAPmax ) and the minimum value ( TXOP _QAPmin ) in the _QAP .

If the channel utilization rate is high, it means that many UEs continue to transmit data packets by performing channel contention, thereby improving network performance by reducing the TXOP limit.

In addition, if the channel utilization rate is low, the TXOP limit is increased so that the UE can transmit many packets through one backoff process.

Therefore, if the measured channel utilization is higher than the upper limit, TXOP _QAP is set to TXOP _QAPmin . Conversely, if the measured channel utilization is less than the lower limit, TXOP _QAP is set to TXOP _QAPmax .

The QAP calculates the TXOP _QAP value using the channel utilization rate obtained from Equations (1) and (2) between the upper and lower channel utilization ratios as follows.

&Quot; (3) "

&Quot; (4) "

The reason for adding TXOP _QAPmin in Equation (4) is to ensure that the calculated TXOP _QAP is always larger than the TXOP _QAPmin .

As shown in FIG. 2, the reason why the upper limit of the channel use rate is selected close to the maximum usage rate is to use the channel as much as possible, and the lower limit of the channel use rate is selected to be about the middle value rather than the low value. There is no difficulty in transmitting the traffic of all the terminals within the delay limit, and the fairness problem does not occur.

The QAP transmits the TXOP _QAPmin value obtained in the above process to all the terminals through the beacon frame. The process of calculating the TXOP _QAPmin value according to the channel usage rate in the QAP is as shown in FIG.

In the process of calculating the TXOP _STA to be used by each UE, the TXOP _STA is calculated by using the TXOP _QAP obtained through the beacon frame transmitted by the _QAP and the UE utilization rate of the UE. Each terminal calculates a queue utilization rate ( Q_Util ) after receiving a beacon frame. This is a value indicating how much data packets are stored in the queue and is calculated as follows.

&Quot; (5) "

Where Q _size is the maximum number of packets the queue can store, and Q _packet is the number of packets currently stored in the queue.

As in the channel utilization calculation, the queue utilization rate is calculated as follows using the moving average window to reflect the traffic generation pattern.

&Quot; (6) "

Here, Q_Util _current is the n-th beacon frame is received after the queue usage rate measurement, Q_Util _{n -1} n -1 is the second beacon and a moving average value calculated after the frame is received, Q_Util _n is computed after moving the n-th beacon frame received average Value.

4, the usage rate increases rapidly as the number of terminals increases, converges to the maximum size of a queue, and the number of terminals increases as the number of terminals increases The longer the waiting time for collision and transmission, the greater the amount of newly generated packets than the transmitted packet amount. Therefore, the amount of packets waiting to be transmitted to the queue increases. Also, packets generated beyond the maximum size of the queue are discarded.

To calculate TXOP _STA we define three new parameters. ( Q_Util _high ) and a lower limit ( Q_Util _low ) of the queue usage rate, and a TXOP limit minimum value ( TXOP _STAmin ) in the terminal.

Each terminal computes the TXOP _STA value using the queue utilization rate obtained from Equations (5) and (6). This procedure is similar to the procedure in which the _QAP computes the TXOP _QAP using the channel utilization.

In addition, if the queue utilization rate is high, it means that many data packets are stored in the queue. Therefore, the TXOP limit is increased to satisfy the delay limit of the packet.

Therefore, if the measured queue utilization is higher than the upper limit, the TXOP _STA is set to TXOP _QAP . Conversely, if the measured queue utilization is less than the lower limit, the TXOP _STA is set to TXOP _STAmin . If the queue usage rate is between the upper and lower bounds, it is calculated as follows.

[Equation 7]

&Quot; (8) "

The reason for adding TXOP _STAmin in Equation (8) is to ensure that the calculated TXOP _STA is always greater than the TXOP _STAmin .

As shown in FIG. 4, it can be seen that the difference between the upper limit value and the lower limit value of the queue utilization rate is not large. If the UE does not transmit all the packets in the queue during a given TXOP limit, the queue usage rate will continue to increase. Therefore, the upper limit is set low so that the terminal has a large TXOP limit. This allows the UE to quickly transmit the packet. The process of calculating the TXOP _STA according to the queue utilization rate of each UE is as shown in FIG. 5.

Meanwhile, the present invention is simulated and the performance is compared with the IEEE 802.11e EDCA method. The simulation parameters used in the simulation are shown in Table 1.

The simulation computes the average after 10 iterations for 30 seconds. In the IEEE 802.11e standard, the TXOP limit value is given as a time length, but expressed as the number of data packets that can be transmitted for convenience of simulation.

Therefore, the TXOP _STAmin value for the method of the present invention is a time for transmitting two data packets. The TXOP _QAPmax value is a time for transmitting 10 data packets. The TXOP _QAPmin value is a time for transmitting 8 data packets Setting.

On the other hand, for IEEE 802.11e EDCA, it is set as the time to transmit fixed 5 packets, the smoothing factor is 0.9, and the delay limit of the multimedia data packet is set to 33 ms. The packet is discarded if it is not delivered to the receiving terminal within the given 33ms.

The size of the multimedia data packet is 1500 bytes, and Exponential Distribution is used to obtain the arrival time interval of the data packet. This distribution has an arrival rate parameter λ and the average arrival time interval is 1 / λ.

The number of terminals used in the simulation is, for example, 1 to 10, and the terminals are divided into two groups in half. In order to set the amount of multimedia traffic to be transmitted by the terminals belonging to each group differently, λ is set as shown in Table 2, and the average arrival time interval of one terminal of the group 1 is 2326us (λ = 0.00043).

Therefore, this terminal has a data generation rate of 5.16 Mbps. The average arrival time interval of one terminal in group 2 is 1587us (λ = 0.00063) and the data generation rate is 7.56Mbps.

parameter value Simulation Time 30 s Beacon Period 100 ms TXOP _QAPmin 8 TXOP _QAPmax 10 TXOP _STAmin 2 Delay Bound 33 ms Q_Util _high 0.20 Q_Util _low 0.05 Queue Size 100 Smoothing Factor 0.9 C_Util _high 0.95 C_Util _low 0.75

Arrival interval time (us) Data rate (Mbps) Group 1 0.00043 5.16 Group 2 0.00063 7.56

Here, [Table 1] is a simulation parameter and [Table 2] is a multimedia data rate of each terminal.

The performance factors used to compare and analyze the simulation results are as follows.

- Channel Utilization: Indicates the time ratio used by the channel for data transmission.

- Normalized Throughput means the amount of data successfully transmitted divided by the capacity of the medium.

- DBSR (Delay Bound Success Ratio): This is the ratio of the number of successfully completed packets satisfying the delay limit for the total number of data packets transmitted to the receiving terminal.

- Standard Deviation of Delay Bound Success Ratio (DBSR-SD): Standard deviation of DBSR.

- Queue Utilization: The ratio of the number of queued packets to the queue size.

The C_Util _low and C_Util _high values are determined using the results of the simulation performed on the TXOP limit of the IEEE 802.11e EDCA. As shown in FIG. 6, the channel utilization ratio and the transmission success rate standard deviation result according to the increase in the number of terminals are shown. The value is set to 0.75, which is the point at which the fairness problem starts to occur due to an increase in the standard deviation of the transmission success rate within the delay limit from 4 or more, and the value is set to 0.95 where the channel utilization rate starts to converge to the maximum value.

The values Q_Util _low and Q_Util _high are determined using the results obtained in the same environment as shown in FIG. Figure 7 illustrates a queue utilization and DBSR-SD result of the terminal increase in the number, the value is set to a single point of 0.05 for the TXOP limit the terminal it is unable to transmit a packet to create a queue usage rate to zero, and Q_Util _high is the terminal The DBSR-SD increases rapidly in the interval from 5 to 6, so it is set to 0.2.

As described above, the present invention adjusts the TXOP limit value dynamically in consideration of channel utilization and queue utilization, and when the overall channel utilization of the network is low, the ratio of unused channels is higher. Since the data packet transmission can be accommodated, a larger TXOP limit can be allocated to a terminal having a large number of packets in the queue, thereby allowing more data packets to be transmitted, thereby reducing the channel contention rate.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. , Alteration, substitution or addition, etc.

Claims (5)

A method for improving the fairness of multimedia traffic in an IEEE 802.11e wireless LAN,
Calculating a transmission opportunity (TXOP) limit using channel utilization information of a network in a QAP (QoS Accese Point);
QAP is a second step of transmitting the TXOP limit obtained in the first step to all the terminals through the beacon frame; And
And a third step of calculating the TXOP limit actually used according to the TXOP limit obtained by each terminal receiving the beacon frame and its own queue utilization (Queue Utilization).
The method of claim 1,
In the first step,
Further comprising the step of measuring the channel usage time during the beacon frame cycle time through carrier sensing in the QAP,
The channel usage rate is calculated by dividing a channel busy time by a beacon frame transmission period, and the busy time is a time when a channel is used regardless of whether the transmission is successful when each terminal transmits a packet A method for improving the fairness of multimedia traffic in a wireless LAN.
[Equation 1]

Where C_Util is the channel usage rate, Busy is the channel busy time, and BeaconPeriod is the period of the beacon frame.
3. The method according to claim 1 or 2,
In the first step,
Since the channel use rate fluctuates very irregularly every time the calculation is performed, the network performance is deteriorated when the calculated value is used as it is, so that the calculation is performed by using the moving average window. ≪ EMI ID = How to Improve the Fairness of Multimedia Traffic in LAN.
&Quot; (2) "

Here, C_Util _current is the n-th beacon frame period calculated by measuring the channel utilization, C_Util _{n -1} n -1-th beacon frame is a moving average value calculation cycle after, C_Util _n is computed after moving the frame (n) th beacon period average And α is a smoothing factor, which is a value of [0, 1].
The method of claim 3, wherein
In the third step,
Wherein the queue usage rate ( Q_Util ) is a value indicating how much data packets are stored in the queue, and is calculated using Equation (5).
&Quot; (5) "

Where Q _size is the maximum number of packets the queue can store, and Q _packet is the number of packets currently stored in the queue.
5. The method of claim 4,
In the third step,
Wherein the queue usage rate is calculated by Equation (6) using a moving average window to reflect a traffic generation pattern.
&Quot; (6) "

Here, Q_Util _current queue is measured after the (n) th beacon frame received usage, Q_Util _{n -1} is the n -1-th beacon frame is received after the moving average value computation, Q_Util _n is the moving average value calculated after the n-th beacon frame received .

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