KR20110114160A - H.264/svc video broadcasting in an wireless local area network with ieee 802.11e hcca mac and multiple datarate phy - Google Patents

Abstract

The present invention devised an effective broadcasting method of H.264 / SVC video stream in IEEE 802.11 based wireless network. The inventive method compresses the video to be broadcasted into H.264 / SVC codec to have multiple layers, and changes the transmission rate according to the importance of video data in the IEEE 802.11e HCCA-based AP. Although there is a difference, there is an advantage that the continuous service is possible to play on all terminals as possible. The inventive method having such advantages can provide an effective video broadcasting service when a temporary wireless network facility is installed, as well as a performance hall, an exhibition hall, a campus, a hotspot, and the like. In addition, the present invention is free to adjust the function and performance of the AP according to the requirements of the video broadcast service provider, wireless terminal users can be used by anyone only by installing a dedicated playback player.

Description

Scalable video broadcasting in a wireless network using an 802.11 WLAN media control layer and a multi-rate physical layer {H.264 / SVC Video Broadcasting in an Wireless Local Area Network with IEEE 802.11e HCCA MAC And Multiple Datarate PHY}

The present invention devised an effective broadcasting method of H.264 / SVC video stream in IEEE 802.11 based wireless network. More specifically, an effective method of broadcasting video in real time using the latest video compression technology, H.264 / SVC codec, to multiple wireless terminals in different communication environments in a widely used IEEE 802.11 wireless network. It is about.

The IEEE 802.11 Wireless Local Area Network (WLAN) standard is the only successful commercialization and is widely used worldwide. The IEEE 802.11 Working Group (WG) introduced the initial standard in 1997, and later added the 802.11a / b standards in 1999 and 802.11g standards in 2003 as the high-speed physical layer (PHY). Recently, 802.11e Medium Access Control (MAC) protocol was added in 2005 to improve the quality of service (QoS) performance for efficient transmission of real-time multimedia traffic and efficient resource usage.

Hybrid Coordination Function (HCF) of 802.11e MAC is divided into competitive Enhanced Distributed Channel Access (EDCA) and non-competitive HCF Controlled Channel Access (HCCA). The HCCA grants the Transmission Opportunity (TXOP) required by the wireless terminal based on polling, which is a non-competitive method, for effective transmission of real-time multimedia traffic. HCCA requires a coordinator for polling control, which is called Hybrid Coordinator (HC). The HC includes an admission controller for determining whether to accept the TXOP request of the wireless terminal and a scheduler for controlling TXOP polling. These are very important features for determining the performance of HCCA, but the 802.11e standard defines them as optional, but provides a reference model to aid implementation.

Since 1990, Motion Picture Experts Groups (MPEG) has introduced video compression standards such as MPEG-1, MPEG-2, and MPEG-4, while International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) has introduced H.261, H.263. Came out. It is significant that the two groups go through standardization together. This gives us a guess as to which direction multimedia services will evolve in the future.

MPEG mainly aimed at high quality video as the goal was to watch video, and ITU-T had to transmit video in real time over the network, so much consideration was given to errors and delays that could occur in the network, dealing mainly with low bit rate coding. It was. However, in the future, as the communication network becomes wider, the low bit rate coding of ITU-T has gradually increased the bit rate. Since a heterogeneous network, in which a broadcasting network and various communication networks interwork, has emerged, two groups have met as MPEG considers a service using such a network. That is, the common goal is to provide a service for transmitting high quality video to a communication network.

Scalable Video Coding (SVC) is a coding scheme suitable for such an environment. In other words, one video is coded into several bit streams and transmitted according to a situation. For example, if you coded five bit streams in five layers, you would send only one bit stream when the situation was bad, one or two bit streams when better, and three bit streams when better. The higher the bit rate in the order of 1, 1 + 2, 1 + 2 + 3, 1 + 2 + 3 + 4, 1 + 2 + 3 + 4 + 5, the higher quality video can be transmitted. This method was also used in the MPEG-2 standardized in 1994. However, since the system was developed only to the extent that digital video transmission is possible through a communication network, it was not actually used. In MPEG-4, called Fine Grain Scalable Coding (FGS), the standardization method is not to jump 1, 2 or 3, but to gradually increase the bit rate and to increase the image quality. The current SVC has not changed much from this past method, but as the current network environment is changed to a mixed communication network, it has attracted extraordinary attention.

There are basically three ways. Temporal scalable coding, spatial scalable coding, and quality layered (SNR scalable coding or quality scalable coding). Temporal tiering sends 7.5 frames per second (16 frames per second) when the network conditions are good, then sends 15 frames per second when the situation improves and 30 frames when the situation improves. It is a very simple method, but the variable bit rate is reduced by about 2 to 3 times the maximum bit rate. Spatial layering transmits the screen size to 100x100 if the network conditions are bad, 200200 if better, and 400x400 if better. The most complicated of the layering schemes, but the maximum bit rate is about 10 times more than the lowest bit rate, so the variable width of the bit rate is very excellent.

[Document 1] Application No. 10-2007-0132722, "Load Balancing System and Method for H.264 SBC Multimedia Data in Wireless Home Network" [Document 2] Application No. 10-2009-0038012, "802.11 Polling and Queue Management Scheme for Guaranteeing Bandwidth Per Session"

[1] Yaser Pourmohammadi Fallah, Panos Nasiopoulos, Hussein Alnuweiri, "Efficient transmission of H.264 video over multirate IEEE 802.11e WLANs," EURASIP Journal on Wireless Communications and Networking, Vol. 2008, Jan. 2008.

There are two ways to broadcast live video in a single network. First, all the terminals can be point to point (unicast) to make it appear that they are actually being broadcast at the same time. Another method is to uniformly receive data when all terminals are connected to one physical transmission medium.

Unlike wired wires, wireless terminals usually change the modulation method automatically according to their communication environment, so that more efficient data transmission is possible. However, due to the limited bandwidth for repeatedly transmitting a large amount of data per unit time, such as a video, it can be broadcast only to a very limited terminal.

The second method is unlimited in the number of terminals since the same data is received by all wireless terminals at once. On the other hand, when the communication environment of wireless terminals is large, it is very difficult to determine an appropriate transmission speed and video compression method. For example, high transmission speeds and low compression rates of high image quality make it difficult to decode correctly even when a remote wireless terminal receives a signal. Conversely, low transmission speeds and high video extrusion rates for distant wireless handsets will only provide bandwidth and low quality video to nearby wireless handsets.

The present invention has devised a way to effectively broadcast video to a plurality of wireless terminals in different communication environments. Specifically, the method of the present invention allows the wireless terminal to be transmitted at an appropriate transmission rate according to importance, so that the wireless terminal can be reproduced using only the video data correctly received without limiting the number of wireless terminals. In other words, the wireless terminal in a superior communication environment enables the viewing of the best quality video, and the wireless terminal in a poor communication environment enables the viewing of the video even though low quality.

The onset requires the IEEE 802.11e HCCA MAC protocol and the H.264 / SVC codec, the latest video compression technology. IEEE 802.11 WLAN is a network base for applying the method of the invention, and consists of a physical layer and a media control layer. Since .11, which initially supports up to 2Mbps, is not currently used in the physical layer, a device applying the .11a / b / g / n standard can be used. However, .11a / g / n, which supports up to 54Mbps, is suitable for serving high-definition video in the inventive way. In addition, the physical layer has an automatic adjustment function so that data can be transmitted by selecting an appropriate modulation method within a usable range according to a wireless communication environment of the terminal. The media control layer includes a distribution coordination function (DCF), a point coordination function (PCF), an EDCA, and an HCCA. Among the methods of the present invention, an access point (AP) equipped with an HCCA and a wireless terminal are required. Although .11n's advanced media control technology has recently been standardized, it has not been applied to commercial products yet.

The H.264 / SVC codec compresses and decompresses video, and as the latest technology, its compression efficiency is superior to existing codecs. Moreover, the H.264 / SVC codec can be played back in one compression and its compressed video in various qualities (quality, refresh rate, screen size). By applying this technique, the inventive method varies the transmission according to the importance among the entire compressed video data. In other words, the transmission speed is changed according to the importance of the data, so that the terminal in the place where the wireless communication environment is not good can receive the minimum data.

H.264 / SVC video, which is divided into layers and compressed, is passed through an AP to be broadcast in an IEEE 802.11 WLAN. As mentioned above, the inventive AP is equipped with .11e HCCA, so as to secure appropriate bandwidth for stable broadcasting of the video. At this time, the AP has a function for identifying a layer of the video and a queue for temporarily storing the separated video data for each layer for differential transmission of each layer of the H.264 / SVC video.

The inventive method is an intermediate form between broadcasting using the existing point-to-point method and broadcasting based on a fixed transmission rate, thereby compromising both advantages and disadvantages. Point-to-point broadcasting can transmit data according to the modulation and transmission speed suitable for each wireless terminal, but because the broadcasting must be repeatedly transmitted, the bandwidth is wasted. Also, if the amount of data to be broadcast is large, the number of radio terminals that can be received is very limited due to the given total bandwidth range.

The fixed transmission rate based broadcasting method cannot but transmit in consideration of the communication environment of all wireless terminals, so it has no choice but to broadcast at a specific transmission rate. For example, if a remote terminal is set as the broadcast standard, all the video data transmissions are determined based on the terminal, and thus a lot of transmission bandwidth is wasted. On the contrary, if the near terminal is a reference, the far terminal has a lot of errors and may be discarded during the media control layer or the video restoration process, or the video playback may be stopped.

The inventive method compresses the video to be broadcasted into H.264 / SVC codec to have multiple layers, and changes the transmission rate according to the importance of video data in the IEEE 802.11e HCCA-based AP. Although there is a difference, there is an advantage that the continuous service is possible to play on all terminals as possible. The inventive method having such advantages can provide an effective video broadcasting service when a temporary wireless network facility is installed, as well as a performance hall, an exhibition hall, a campus, a hot spot, and the like. In addition, the present invention is free to adjust the function and performance of the AP according to the requirements of the video broadcast service provider, wireless terminal users can be used by anyone only by installing a dedicated playback player.

1 is an explanatory diagram for explaining the basic operation of the invention system;
2 is a structural diagram illustrating a Network Abstraction Layer (NAL) packet format of H.264 / SVC video.
3A is a structural diagram illustrating a queue management scheme of an existing IEEE 802.11e HCCA.
3B is a structural diagram illustrating an HCCA queue management scheme in a wireless terminal.
4A and 4B are structural diagrams illustrating a method of inputting H.264 / SVC video data into an AP of the present invention.
5 is a structural diagram illustrating a method of coexisting with the existing HCCA TSPEC and H.264 / SVC video broadcasting method.

Details and methods of the present invention can be described by the accompanying drawings and formulas. Figure 1 is intended to briefly represent the manner of the invention as a whole. The transmission rate 101 means which modulation method is applied when the wireless AP using the inventive method broadcasts H.264 / SVC video data to the wireless terminals. That would be 6, 9, 12, 18, 24, 36, 48, and 54 Mbps if you were using .11g. The distance 102 means a distance at which data transmitted by an AP arrives at a wireless terminal and can be normally received. For typical home and small office applications, .11g can transmit 100 meters outdoors at the lowest speed. When the videos made by H.264 / SVC codec are classified into NAL units from L ₀ to L _n , if they are transmitted one by one, the most important L ₀ can be transmitted to the farthest wireless terminal at the lowest transmission rate. The NAL of L _n , which is considered to be the least important, is transmitted at the fastest speed at the last time so that only nearby wireless terminals can use it to play high resolution video. However, L ₀ to L _n do not mean the number of layers, but are reordered according to the order determined in the onset of disease. In general, the closer to L _n , the greater the amount of video data in the layer.

2 is a NAL format used as a data division unit of an H.264 / SVC video. The inventive method looks at the values of screen size 201, image quality 202, and refresh rate 203 to determine the characteristics and importance of the NAL. 3A depicts a method used in an existing IEEE 802.11e HCCA transmission. The unused TIDs 3a1 of FIG. 3 are used for background and best traffic, while the HCCA has two TIDs each for video 3a2 and 3a3 and voice transmission. However, two TIDs are insufficient to process multiple video streams, which may cause a problem. For details, refer to Patent Document [Document 2] among the prior art documents filed prior to the present invention.

FIG. 3b illustrates a method of filing an application (patent document 2) invented to modify the existing IEEE 802.11e HCCA to extend the TID and the corresponding queue as desired. When wireless terminal number 1 is simultaneously transmitting or receiving two video streams, each video is assigned a corresponding queue (3b1, 3b2), and is divided into a pair of TSI numbers and numbers instead of the media control layer address of the wireless terminal. . By applying this method, up to 15 video sessions can be sent or received for maximum video per terminal, so the AP using the inventive method can allocate enough HCCA queues by accurately identifying enough video sessions. have. On the contrary, since the streaming amount of data does not change drastically like a video, the allocation of only one TSI and HCCA cue 3b6 does not cause a problem in video transmission. In this way, independent management of each video session and HCCA queue allocation can strongly guarantee video by session.

There are two main methods of transmitting H.264 / SVC video data, as shown in FIGS. 4A and 4B. FIG. 4A transmits using one port in the transport layer, and when NAL packets 4a1 are received by the AP of the invention scheme, the HCCA queues 4a2 and 4a3 are distinguished according to importance and characteristics with reference to the NAL format of FIG. 2. , 4a4). 4b is also possible when using multiple transport layer ports, the method of FIG. 4a is possible, but the NAL packets 4b1, 4b2, 4b3 associate the port number of the transport layer with the HCCA queues 4b4, 4b5, 4b6. Can be entered. H.264 / SVC video may insert the Suplemental Enhancement Information (SEI) into the front of the video bit stream or periodically in the middle of the bit stream. The SEI includes information such as a compression method of the video content. The method of the present invention generates the HCCA queue by identifying the SEI and referring to the number and importance of video layers and the average data generation rate for each layer.

To summarize the manner of the invention can be described as shown in FIG. NAL packets transmitted using a single 501 or multiple transport layer ports are input to the HCCA queue using a patented method in order to guarantee a strong bandwidth for each video session. In particular, since H.264 / SVC video is divided into several layers, video data can be more effectively provided for broadcasting or point-to-point transmission using multiple HCCA cues.

The total TXOP time sum of the IEEE 802.11e HCCA should be less than the time between beacon frames except the contention period. In the following Equation 1, the left side determines whether the k + 1 th TXOPs can converge. The ratio of the entire TXOP in the SI (Service Interval), which is the polling period, should be less than the ratio of the non-competition interval (TT _cp ) and the beacon frame time T except the right competition interval T _cp .

The inventive scheme is designed to coexist with existing IEEE 802.11 standards. Equation 2 determines whether convergence includes the TXOP of the existing HCCA and the B_TXOP of the inventive method. Equation 3 is a method of calculating each B_TXOP time. The average MSDU packet length L and its number N for each H.264 / SVC video layer are divided by the transmission rate R to obtain the time, and the overhead O is calculated for each MSDU. The transmission rate R is selected one for each H.264 / SVC video layer among all the standards that can be used by the IEEE 802.11 physical layer. The method of determining the transmission rate of the physical layer for each video layer (per layer data rate) is shown in [Equation 4]. All video data generation rate of the P layer over _all the i-th video data generation rate P _i From the ratio, the smallest R _j is selected among the transmission rates R where the ratio of each R to the maximum transmission rate R _max of the available IEEE 802.11 physical layer is larger. If the obtained B_TXOP time is less than the maximum transmission time of one MSDU at the minimum transmission rate R _min and the transmission overhead of this MSDU, it is replaced by this value.

In the method of the present invention, the packets of a video layer having a high importance are transmitted at a low transmission rate, so that the minimum video reproduction is possible even in a terminal having a poor wireless communication environment. Equation 5 is a method of reordering the H.264 SVC video layer according to importance (per Layer TX Order). The importance of video layers is in order of each screen size (D)> frame rate (T)> quality (Q). There are many criteria for determining importance, but the invention method deals with the basic screen size most importantly for reproducing other enhancement layers, and the frame rate rather than deterioration of image quality. When the D, T, and Q parameters of the NAL packets of the incoming packets are checked and the order of importance is determined by Equation 5, they are input to the corresponding HCCA queue as shown in FIGS. 4A and B. At this time, it is assumed that all MSDUs have D, T, and Q information of the NAL packet header even after all NAL packets input to the AP of the present invention are fragmented.

Claims (6)

As shown in FIG. 1, as an effective small video broadcasting method considering a communication environment of a wireless terminal that can be represented by a distance, a video made to have multiple layers with an H.264 / SVC codec based on an IEEE 802.11 WLAN Broadcasting method that transmits with different transmission speed according to importance.
Method of inputting the NAL packets of the H.264 / SVC video represented in Figure 4a / b 1: 1 mapping to the HCCA transmission queue using the D, T, Q parameters.
Equation 4 as a method for mapping the D, T, and Q parameters of the NAL packet to the HCCA transmission queue in [Claim 2].
As the inter-layer transmission order and method expressed in FIG. 5, a packet having a high priority video layer has a lower transmission rate and a first transmission method.
Equation 4 designed to coexist existing method TXOP and invention method B_TXOP and Equation 5, which is a calculation method of B_TXOP.
Equation 4 as a method of selecting a sufficient transmission rate of the IEEE 802.11 physical layer for each layer of the H.264 / SVC video.

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