KR20140035719A - Fair share scheme of delay margin for real-time multimedia delivery in wireless lans - Google Patents

Abstract

The present invention relates to a fair share method of delay margin for real-time multimedia transmission in wireless local area networks and, more specifically, to the fair share method comprising: a first process for equally sharing the delay margin between the data packets by restricting the retransmission attempt number of the data packet including long residual delay restriction for supporting real-time multimedia traffic including different residual delay restriction, and a second process for determining the residual delay restriction of a block for calculating the delay margin. The delay margin is the residual time of the residual delay margin after transmitting the data packet. The block is a group of the data packets transmitted during transmission opportunity (TXOP) time in an IEEE 802.11e MAC protocol by a terminal. Therefore, the present invention may share the delay margin for the real-time multimedia transmission in the wireless local area networks by restricting the retransmission attempt number of the data packet considering the residual delay restriction of the all data packets existed in all data packets and by equally sharing the residual delay restriction between the data packets.

Description

{Fair Share Scheme of Delay Margin for Real Time Multimedia Delivery in Wireless LANs}

The present invention relates to a method and apparatus for distributing a residual delay bound in a multimedia transmission in a wireless LAN environment equally between data packets and limiting the number of retransmission attempts of data packets in consideration of a residual delay limit of all data packets in a queue To a delay margin sharing method for real-time multimedia transmission in a LAN.

Currently, the transmission of real-time multimedia traffic over a wireless LAN faces several problems. This is because multimedia traffic has a strict quality of service (QoS) requirement for delay and loss.

In particular, ensuring a delay bound is very important for real-time multimedia traffic. Multimedia data packets in the UE's queue may have different delay limits.

If the terminal uses a lot of time to transmit a data packet with a long delay limit, other packets in the queue are delayed. This is because the IEEE 802.11 medium access control (MAC) protocol transmits packets in a first in first out (FIFO) manner.

Therefore, a data packet having a short delay limit is discarded because it does not satisfy its delay limit, and a data flow having a long delay limit has a better performance than a data flow having a short delay limit.

On the other hand, the data packets in the terminal largely have different residual delay limits for three reasons. First, since the delay limit between data packets is different according to the characteristics of multimedia traffic, the traffic has various characteristics. Thus, the data packet has different end-to-end delay limits and residual delay limits. Second, each data packet has different transmission times because it is transmitted over the network through various paths. Third, the delay experienced by the data packet depends on the distance between the multimedia server and the terminal. If the server and the terminal are close, the data packet will have a short transmission delay time, and if it is far away, it will have a long transmission delay time.

In such an environment, if an 802.11 terminal transmits a data packet to a receiving terminal without an additional method, a fairness problem occurs between data packets. A data packet having a long residual delay limit can be transmitted to a receiving terminal with high probability because it can make multiple retransmission attempts within its own delay limit.

However, a packet with a short residual delay limit has a low probability of successful transmission due to a small retransmission attempt. Another problem is that when a data packet having a long residual delay limit is located at the head of the queue and retries a number of retransmissions, other packets following the long packet are subjected to a long delay, and the probability of being transmitted within their remaining delay limit is reduced. Therefore, a flow having a long residual delay limit has better performance than a flow having a short residual delay limit. This causes a problem of inequality between data packets or between flows.

Figure 1 is an illustration showing an inequity problem.

As shown in FIG. 1, when there are three data packets in the UE's queue and each remaining delay limit is RDB1, RDB2, and RDB3, Packet 1 must be transmitted to the receiving terminal first because it is at the head of the queue. Two retransmissions were made within the residual delay limit due to the collision. That is, packet 1 was successfully delivered to the receiving terminal in the third transmission.

Since the terminal has used too much channel time to transmit the packet 1, the packet 2 does not have its remaining delay time at the completion time of the packet 1 and can not even attempt to transmit it, but is immediately discarded. Packet 3 has only one chance to try. Therefore, packet 1 causes unfairness for packets 2 and 3.

S. Sheu and T. Sheu, A bandwidth allocation / sharing / extension protocol for multimedia over IEEE 802.11 Ad Hoc wireless LANs. IEEE Journal on Selected Areas in Communications. Vol. 19, No. 10, (2001), 2065-2080. B. Hamdaoui, M. Elaoud, and P. Ramanathan, A delay-based admission control mechanism for multimedia support in IEEE 802.11e wireless LANs. Wireless Networks. Vol. 15, No. 7, (2009), 875-886. Q. Deng and A. Cai, A TXOP-based scheduling algorithm for video transmission in IEEE 802.11e networks, Proceedings of the 6th International Conference on ITS Telecommunications, (2006), 573-576. 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.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for distributing a residual delay bound in a multimedia transmission in a wireless LAN environment among data packets, The present invention has an object of providing a delay margin sharing method for real time multimedia transmission in a wireless LAN by limiting the number of retransmission attempts of data packets in consideration of a limit.

The delay margin sharing method for real-time multimedia transmission in a wireless LAN according to the present invention for achieving the object of the present invention, in the fair sharing method of the delay margin for real-time multimedia transmission in a wireless LAN, different residual delay limits A process of equally dividing a delay margin between data packets by limiting the number of retransmission attempts of a data packet having a long residual delay limit to support real-time multimedia traffic having a; And determining the remaining delay limit of the block to calculate the delay margin, wherein the delay margin is the remaining time of the residual delay limit after transmitting the data packet, and the block is an IEEE 802.11e MAC. In the protocol, the terminal is a group of data packets to be transmitted during a Transmission Opportunity (TXOP) time.

If the remaining delay limit of all data packets in the block is greater than the transmission completion time of the block in the step 2, the remaining delay limit of the block is set to the smallest remaining delay limit of the data packets in the block .

If the remaining delay limit of the data packet in the block is larger than the transmission completion time of the block but smaller than the transmission completion time of the block in the above step 2, the residual delay limit value of the block is set as the transmission completion time of the block And the remaining delay limit of all the data packets is satisfied even if the residual delay limit of the block is set in the step 4 above.

If the remaining delay limit of the data packet in the block is smaller than the transmission completion time of the data packet in the step 2, the residual delay limit of the block is set as the smallest residual delay limit value in the data packet .

The present invention is characterized by calculating the delay margin for each block by [Equation 2].

&Quot; (2) "

Where DM _i is the delay margin of the i- th block in the queue, RDB _i is the residual delay bound, CAD is the channel access delay, and BLOCK_TX _i is the block transmission time transmission time).

As described above, the technical problem solving pursues in the present invention is to divide the residual delay bound equally between data packets and to increase the number of retransmission attempts of the data packet considering the remaining delay limit of all the data packets in the queue It is possible to share a delay margin for real-time multimedia transmission in the wireless LAN.

Figure 1 is an illustration showing a conventional inequity problem.
2 (a), 2 (b) and 2 (c) are diagrams showing the residual block delays according to the present invention.
FIG. 3 is a flowchart illustrating a delay margin sharing method for real-time multimedia transmission in a wireless LAN according to the present invention.
4 is a diagram illustrating a simulation topology according to the present invention.
5 is a diagram illustrating a transmission failure rate according to a residual delay limit of a short flow sphere according to the present invention.

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

FIG. 2 is a diagram illustrating a block residual delay limit according to an embodiment of the present invention. FIG. 3 illustrates a delay margin sharing method for real-time multimedia transmission in a wireless LAN according to the present invention. And FIG. 4 is a diagram illustrating a simulation topology according to the present invention.

As shown in FIGS. 1 to 3, a delay margin sharing method for real-time multimedia transmission in a wireless LAN according to an embodiment of the present invention begins with a backoff counter value of 0 Is defined as the channel access delay.

The CAD (channel access delay) is updated every time the channel competition wins. The terminal measures the CAD value in the nth channel competition and displays it as CAD current. Then, CADn is calculated as follows using a moving averaging window.

[Equation 1]

Here, CADn-1 is the updated channel access delay after the (n-1) -th channel contention, and? Is a smoothing factor having a value between [0, 1].

To support real-time multimedia traffic with different residual delay limits, the Fair Share of Delay Margin (FSDM) of the present invention limits the number of retransmission attempts of data packets with a long residual delay limit.

This is a way to equally distribute the delay margin between data packets. The delay margin represents the remaining time of the remaining delay limit after transmitting the data packet.

In the IEEE 802.11e MAC protocol, a terminal can transmit multiple data packets continuously during TXOP time. Here we define a new term block. A block is a group of data packets to be transmitted during the TXOP time.

To calculate the delay margin, the residual delay limit of the block must first be determined. To determine this, three possible cases have to be considered, as shown in Figures 2 (a), (b) and (c). 2 (a) shows the case where the remaining delay limit of all the data packets in the block is larger than the transmission completion time of the block, and the remaining delay limit of the block is set to the smallest remaining delay limit of the data packets in the block.

2 (b) shows a case where the remaining delay limit of the data packet in the block is larger than the transmission completion time of the block, but is smaller than the transmission completion time of the block. In this case, the residual delay limit value of the block is set to the transmission completion time of the block. Even if the residual delay limit of the block is set as above, the remaining delay limit of all data packets is satisfied.

Third, FIG. 2 (c) shows a case where the remaining delay limit of the data packet is smaller than the transmission completion time of the data packet. In this case, the remaining delay limit of the block is set to the smallest remaining delay limit value in the data packet.

On the other hand, assuming that the data blocks in the queue are transmitted without retransmissions, the delay margin for each block is calculated as follows.

&Quot; (2) "

Where DM _i , RDB _i , and BLOCK_TX _i are the delay margin, residual delay bound, and block transmission time of the ith block in the queue.

BLOCK_TX the basic approach is the (ACK + DATA + 2SIFS) * TXOP_PKT BLOCK_TX and the RTS / CTS approach is RTS + CTS SIFS + + (+ 2SIFS DATA + ACK) * TXOP_PKT.

DATA, RTS, CTS, and ACK respectively indicate transmission time of DATA, RTS, CTS, and ACK. SIFS denotes the SIFS time, and TXOP_PKT denotes the TXOP expressed by the number of data packets, not the time length.

After calculating the delay margin (DM) value for all blocks, the proposed method converts the DM to RDM (Retransmission Delay Margin).

RDM is the DM expressed by the number of retransmissions and is transformed as follows.

&Quot; (3) "

Here, EIFS (Extended Inter-frame Space), DIFS is EIFS, and DIFS time. [x] means the largest value among integers less than or equal to x.

According to the IEEE 802.11e standard, when a collision occurs, the AC delays for EIFS - DIFS + AIFS time before starting transmission. However, in equation (3), the AIFS value is not included. This is because CAD already includes this value.

After calculating the RDM value, the proposed method checks whether there is a block with an RDM value of 0 or less. If it is, set the number of retransmission attempts of the block to zero. This is because the retransmission attempt will cause additional delays in the data packets in the block and the data packets can be discarded because they do not satisfy their residual delay limit.

If the RDM value of all blocks is greater than 0, the FSDM method calculates the fair share unit (FSU). FSU means a fair amount of spare retransmission margin to be allocated to each block. If the retransmission delay margin is allotted to one block without consideration of fairness among the blocks, it will cause unfairness to other blocks due to the retransmission delay of the block. FSU _i of the ith block Is as follows.

&Quot; (4) "

Each block with a block index of i or less has a fair margin of FSU _i . The FSDM method of the present invention must select a minimum value among the FSU values to satisfy the remaining delay limit of all data packets in the queue. The minimum value FSU (MFSU: minimum FSU) is as follows.

&Quot; (5) "

로 계산된다. [x]는 x 이상의 정수 중에서 가장 작은 값을 의미한다. MFSU를 결정한 다음에 FSDM 방법은 블락의 재전송 시도 횟수를 [MFSU]로 설정한다.Where N is the number of blocks in the queue

. [x] means the smallest value among integers greater than or equal to x. After determining the MFSU, the FSDM method sets the number of retransmission attempts of the block to [MFSU].

FIG. 3 is a flowchart illustrating an operation procedure of a fair sharing method of delay margin for real-time multimedia transmission in a wireless LAN according to the present invention. Referring to FIG. 3, the terminal performs this procedure every time the back- do.

4 is a diagram illustrating a simulation topology according to the present invention. The simulation results of the FSDM method of the present invention are analyzed. We propose a conceptual method called DB (Delay Bound) for comparison. After channel access, the DB method checks whether the head packet in the queue satisfies its residual delay limit. If satisfied, it transmits the data packet, discards it if it is not satisfied, and repeats the above process again for the next packet in the queue.

In the simulation, the topology is considered as shown in Fig. There are two types of multimedia and background traffic. There are two real-time multimedia servers on the Internet and two multimedia receiving terminals receive data packets transmitted by the server through the AP.

The residual delays of traffic transmitted by each multimedia server are different. Here we will call short flow and long flow to distinguish each other. 10 background terminals transmit data packets to the AP. Background traffic operates in DCF mode and is used to observe the impact on real-time multimedia traffic. Assuming that all terminals are within the transmission range of each other, there is no channel error.

The system parameters used in the simulation are listed in Table 1. The simulation was performed for an IEEE 802.11a network transmitting data packets at 54 Mbps and ACK, RTS, and CTS packets at 6 Mbps. Only the basic approach is considered in the simulation.

Parameter Value Data Bit Rate (Mbps) 54 Control Bit Rate (Mbps) 6 Slot Time (us) 9 SIFS (us) 16 Retry Limit 7 Propagation Delay (us) One MAC Header (Octets) 26 CRC (Octets) 4 PHY PLCP Preamble Length (us) 16 PHY PLCP Header Length (Octets) 5 ACK (Octets) 14 Queue Size (Packets) 50 Smoothing Factor 0.9

Parameter Multimedia Background AIFSN 4 7 CWmin 15 31 CWmax 31 1023 Packet Size (Octets) 1500 1500 TXOP_PKT 3 One

Here, Table 1 is a simulation parameter, Table 2 is a traffic parameter.

An exponential distribution was used to obtain the arrival time interval of the data packet. The average arrival time interval of the distribution with the arrival rate parameter λ is 1 / λ. The average arrival time of background traffic is 5000 us (λ = 0.0002). Therefore, each background terminal generates data of 2.4 Mbps. The arrival time of real-time multimedia traffic is 2500 us (λ = 0.0004). In order to take account of the burstyness attribute of the multimedia traffic, a value between [1, 5] is arbitrarily selected every data packet arrival time to generate a corresponding number of data packets. Therefore, the transmission rate of multimedia traffic is 14.4 Mbps. The residual delay limit of the long flow is fixed at 20ms and the limit of the short flow changes between 10ms and 20ms.

The main performance factors are normalized throughput and delivery failure ratio. The transmission failure rate does not satisfy the residual delay limit for the total transmitted data packets and represents the ratio of discarded multimedia packets.

5 is a diagram illustrating a transmission failure rate according to a residual delay limit of a short flow sphere according to the present invention.

As shown in Figure 5, both FSDM and DB methods show a similar result pattern. The transmission failure rate gradually increases as the residual delay limit decreases. From the results, it can be seen that the proposed method always has better performance than the DB method. The DB method uses too much channel time to transmit long flow packets. Thus causing additional delays for short-flow packets and reducing the likelihood of meeting the residual delay limit.

However, the FSDM method limits the number of retransmission of long flow packets considering the residual delay limit of all data packets in the queue. Thus reducing the transmission failure rate of short flows. However, as can be seen from the figure, the long flow still has a lower transmission failure rate than the short flow. This is because the FSDM method calculates the DM value based on the CAD obtained through the moving average. The moving average does not always smooth the variation in channel access delay.

In particular, background traffic may affect the CAD value and thus have a channel access delay greater than the CAD value. In this case, the long flow packet can still be successfully transmitted within its residual delay limit, but the short flow packet can be discarded because it does not satisfy its residual delay limit. However, it can be seen that the proposed method reduces the inequity by about 50% compared to the DB method.

As described above, since the residual delay bound is equally divided among the data packets and the number of retransmission attempts of the data packet is limited in consideration of the remaining delay limit of all the data packets in the queue, Can share the delay margin for

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)

In a fair sharing method of delay margin for real-time multimedia transmission in a wireless LAN,
A step of restricting the number of retransmission attempts of a data packet having a long remaining delay limit in order to support real-time multimedia traffic having different residual delay limits, thereby fairly distributing delay margins among data packets;
And a second step of determining a remaining delay limit of the block to calculate the delay margin,
The delay margin is the remaining time of the remaining delay limit after transmitting the data packet, and the block is a group of data packets to be transmitted by the terminal during the Transmission Opportunity (TXOP) time in the IEEE 802.11e MAC protocol. Fair sharing method for delay margin for real-time multimedia transmission in WLAN.
The method of claim 1,
If the remaining delay limit of all the data packets in the block is greater than the transmission completion time of the block in the step 2, the residual delay limit of the block is set to the smallest remaining delay limit of the data packets in the block The method comprising the steps of: (a) storing the delay margin in a wireless LAN;
The method of claim 1,
If the remaining delay limit of the data packet in the block is larger than the transmission completion time of the block but less than the transmission completion time of the block in the step 2, the remaining delay limit value of the block is set as the transmission completion time of the block. Further comprising:
Wherein the remaining delay limit of all the data packets is satisfied even if the residual delay limit of the block is set in step 4 above.
The method of claim 1,
If the remaining delay limit of the data packet in the block is smaller than the transmission completion time of the block in the step 2, setting the residual delay limit of the block to the smallest remaining delay limit value in the data packet A fair sharing method of delay margin for real - time multimedia transmission in wireless LAN.
The method according to any one of claims 1 to 4,
Equivalent sharing method of delay margin for real-time multimedia transmission in wireless LAN, characterized by calculating the delay margin for each block by Equation 2.

&Quot; (2) "

Where DM _i is the delay margin of the i- th block in the queue, RDB _i is the residual delay bound, CAD is the channel access delay, and BLOCK_TX _i is the block transmission time transmission time).

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