JP2008519528A - System and method for transmitting layered video over a QoS enabled WLAN - Google Patents

Abstract

Multi-layer variable rate (VR) having both base layer (BL) packet (608) and upper layer (EL) packet (610) using flow control layer (614) when wireless network is congested Disclosed is a system and method for transmitting layered video over a quality of service (QoS) enabled wireless local area network (WLAN) that discards upper layer (EL) packets from a video stream. An exemplary system includes an encoder (602) suitable for receiving video data and encoding into a video bitstream having both base layer BL packets (608) and upper layer EL packets (610); A flow control layer (612) that can discard one or more of the upper layer EL packets (610) associated with the video stream, depending on the state of the wireless medium, and a scheduler (SE) that schedules the packets (614) and a MAC layer (616) for wireless transmission of the video stream.

Description

  The present invention generally relates to communication systems. In particular, the present invention relates to a system and method for transmitting layered video data over a quality of service (QoS) enabled wireless local area network (WLAN).

  Development of high-quality multimedia devices (set-top boxes, high-end television receivers, digital television receivers, personal television receivers, storage products, personal digital assistants (PDAs), wireless internet devices, etc.) Has led to a higher openness to the various architectures and new features of the devices described above. The development of new multimedia products as described above ensures that the general public will continue to increase demand for multimedia services. Network designers and engineers therefore continue to design systems that can meet the growing demand for real-time and non-real-time multimedia transmissions over integrated networks.

  In recent years, IEEE 802.11 wireless local area networks (WLANs) have emerged as the dominant technology for mobile / portable (indoor) broadband wireless access. The IEEE 802.11 working group supports 802.11e (QoS) to extend the 802.11 application domain by enabling applications such as voice and video services over wireless local area networks (WLANs). (Complementary to 802.11 Medium Access Control (MAC)) was developed relatively recently. The IEEE 802.11e standard provides seamless interoperability across home, business, and public access network environments while still providing features that meet the specific needs of each type of network. Unlike other wireless efforts, IEEE 802.11e adds a QoS feature and multimedia support to the existing IEEE 802.11 standard while maintaining full backward compatibility with legacy standards. It is the first wireless standard that spans the business environment.

  Multimedia traffic QoS support is essential for home wireless networks where voice, audio, and video are distributed over networked home electronic devices and personal computers. Broadband service providers can add QoS and multimedia home networks to subscriber value-added services (video on demand, audio on demand, voice over IP, high speed Internet access, etc.) As an essential element in providing

  In 802.11e, a traffic specification (TSPEC) that characterizes a data traffic stream (eg, data rate, packet size, delay, jitter, service interval, etc.) provides access to the type of wireless networking service that is expected. Used as a signaling mechanism for indicating to a point (AP). The aforementioned traffic stream is delivered to the AP according to the QoS parameters. A TSPEC negotiation between the peer scheduler and the MAC layer provides a mechanism to control the acceptance, setup, adjustment and removal of traffic streams. Traffic stream admission control is particularly important because the available bandwidth in a wireless medium is limited. Bandwidth access must be controlled to avoid traffic congestion (which tends to lower the configured QoS and lead to dramatic degradation in overall throughput).

  For wireless transmission of video data, a scalable representation of a video signal has a base layer (BL) packet and a plurality of upper layer (EL) packets. BL packets provide a basic quality level and can be decoded independently of upper layer EL packets. On the other hand, the upper layer EL packet only serves to refine the quality of the base layer BL packet, and is not useful alone. Thus, since the base layer BL packet represents the most important part of the scalable representation, the performance of a streaming application using a layered representation is highly sensitive to the loss of the BL packet.

  A wireless transmitter with a video encoder is a multi-layer variable rate (VR) video that comprises both a base layer BL packet with data essential for decoding and an upper layer EL packet with data that improves the quality of the video output. Create a stream. Packet frames are transmitted sequentially. The number depends on the variable channel condition. The packet of the frame must reach the receiver to be decoded by the predetermined decoding time of the frame because the packet is available for decoding. Thus, there is an important point in time when non-transmitted packets of a frame can be discarded afterwards because the receiver / decoder is not reached within a predetermined frame decoding time.

  The conventional TSPEC mechanism allows transmission of variable rate VR video streams. However, if the wireless network is unable to comply with the negotiated service level (due to an error), the TSPEC mechanism does not specify when to reject or discard the application. For example, TSPEC does not specify when to reject a data traffic stream between when a single packet is lost and when two or more packets are lost. . Thus, it is impossible (in absolute terms) to guarantee that the communication channel remains error-free in the wireless medium, and a reasonable upper bound on the packet error rate when the residual is zero. The scheduler layer and MAC layer characteristics are not fully defined when a packet is lost because it is equally impossible to define. This means that different implementations behave differently so that at least some of the scheduler / MAC layers may refuse to accept certain traffic streams that are not capable of providing the necessary QoS. Means.

  Accordingly, there is a need in the art for an apparatus and method for maintaining a layered video transmission connection over an unreliable wireless channel in cooperation with existing TSPEC mechanisms.

  The present invention provides a mechanism for using existing TSPEC signaling in 802.11 along with a flow control algorithm to utilize layered representations to achieve flexibility in the presence of time-varying channels and improve overall picture quality. By providing, the aforementioned needs and other disadvantages and / or disadvantages associated with the transmission of layered video data over unreliable wireless channels are addressed. In an exemplary embodiment of the invention, flow control operates to discard higher layer EL packets that do not reach the receiver for decoding before the frame decoding time. Thus, the packet scheduler then schedules the transmission of the base layer BL packet and the remaining upper layer EL packets without having to determine whether to reject the traffic stream due to insufficient QoS. Can do. Thus, according to an advantageous feature of the present invention, the flow control feature provides a means for effectively transmitting layered video data over an unreliable wireless channel.

  QoS enabled, discards upper layer EL packets from multi-layer variable rate VR video stream with both base layer BL packets and upper layer EL packets using flow control layer when wireless network is congested A method according to an illustrative aspect of the present invention for transmitting layered video over a wireless local area network is provided. A system according to another exemplary aspect of the present invention includes an encoder suitable for receiving video data and encoding into a video bitstream having both base layer BL packets and upper layer EL packets, One or more of the upper layer EL packets associated with the stream can be discarded as needed depending on the state of the wireless medium, the scheduler SE for scheduling packets, and the wireless transmission of video streams With a MAC layer.

  Further and / or other aspects, features and advantages of the present invention will become apparent with reference to the following detailed description of exemplary embodiments thereof.

  For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

  Referring to FIG. 1, a wireless local area network (WLAN) prior art exemplary extended service set is illustratively shown. The illustrated extended service set 100 includes a host 110, a distribution system 120, a first quality of service (QoS) basic service set (QBSS) 130, and a second quality of service (QoS) basic service set (QBSS). 140). A typical QBSS 130, 140 has several QoS radio stations (QSTAs) 150 that utilize the same medium access control (MAC) protocol and contend for access to the same shared medium. Each QBSS 130, 140 can be isolated or connected to operate with the distribution system 120.

  As shown in FIG. 1, each QBSS 130, 140 is connected to the distribution system 120 via a quality of service (QoS) access point (QAP) 160. The QAP 160 is a QoS radio station that can be connected to the distribution system 120 to operate. QAP 160 typically operates as a bridge between QBSSs 130, 140 and distribution system 120. The MAC protocol of the QBSS 130, 140 can be fully distributed and / or controlled via a central linkage function within the QAP 160 of the QBSS 130, 140.

  Referring now to FIG. 2, a prior art seven open system interconnection (OSI) network hierarchy is illustratively shown. Each of the foregoing hierarchies is well known in the art and is provided here for reference purposes. The first layer is the physical layer 200. The physical layer 200 is the first layer of the OSI model and operates at the bit stream level or the binary level. The physical layer 200 focuses on electrical impulses and radio signals that travel through and within the actual physical network structure. The second layer is the data link layer 210. The data link layer 210 is typically responsible for packet processing (particularly for bit level packet encoding and decoding). The data link layer 210 is also related to knowing the transmission protocol and error checking aspects for the physical layer 200. The data link layer 210 includes a medium access control layer (MAC layer) that controls access and permission restrictions on data traveling on this layer, and a logical link control layer (LLC) that plays a role of frame synchronization, flow control, and error checking. Layer). The third layer is the network layer 220. The network hierarchy 220 serves to guide and move data within the network. The fourth layer is the transport layer 230. The transport layer 230 primarily serves to ensure complete and effective data movement between the end system and the host. The fifth layer is the session layer 240. Session layer 240 manages and coordinates connections between separate applications that interact with the network and its data. The sixth layer is the presentation layer 250. The presentation layer 250 primarily serves to accurately interpret and display incoming and outgoing data. Finally, the seventh layer is the application layer 260. The application layer 260 is responsible for providing support for end-user processing (eg, addressing quality of service issues).

  FIG. 3 schematically illustrates a prior art frame format 300 for IEEE 802.11e Quality of Service (QoS) data. Each single QoS data frame contains a priority of the prioritized QoS frame, or a traffic identifier (TID) value that identifies the corresponding traffic stream of the parameterized QoS. To accommodate the aforementioned information, the IEEE802,11eQoS data frame header has two QoS control fields 310 of octets. The QoS control field 310 indicates a TID value using 4 bits and also contains other specific QoS related information. Typically, two types of QoS operation management frames are defined for setting up, modifying, and deleting traffic streams. The first type includes a TS request addition operation frame and a response QoS operation frame for setting and / or modifying a QoS stream. The second type includes a TS request deletion operation frame and a response QoS operation frame for deleting a QoS stream. Each QoS operation management frame indicates a traffic specification (TSPEC) information element for conveying a corresponding QoS requirement and traffic specification.

  An illustrative prior art frame format for a traffic specification (TSPEC) element is schematically illustrated in FIG. The TSPEC element 400 is a one-way traffic in the context of a specific radio station (WSTA) for use by a hybrid coordinator (HC) and a radio station (WSTA) to support parameterized QoS traffic forwarding. It has a parameter set that defines the stream characteristics and QoS expectation values. A normal TSPEC element information field has items shown in FIG. The TSPEC element 400 allows a wider range of parameter sets than may be necessary, or may be available in any particular case of parameterized QoS traffic. The field is set to 0 if no parameter value is specified. The recommended parameters for the TSPEC element include the average bit rate for packet transmission, maximum delay allowed for packet transmission, nominal packet size, prioritization for packet transmission, maximum packet size, and maximum data at peak rate. There is a burst size, a minimum transmission rate of the physical layer, and a maximum bit rate of packet transfer. TSPEC negotiation between peer MAC layers provides a mechanism to control the acceptance, setup, adjustment and removal of traffic streams. There is limited bandwidth available in the wireless medium to minimize traffic congestion (which can cause the configured QoS to be lowered and cause significant degradation in overall throughput) If this is the case, this traffic stream acceptance becomes important.

  Turning now to FIG. 5, an exemplary prior art architecture 500 of a quality of service (QoS) radio station (QSTA) is illustratively shown. As shown, a station management entity (SME) 502 extends from the application layer 260 to the physical layer 200. The physical layer 200 is represented by a physical layer convergence protocol (PLCP) 504 and a physical layer management entity (PLME) 506 as shown. The medium access control layer (MAC layer) 508 is above the physical layer convergence protocol (PLCP) 504 and the MAC layer management entity (MLME) 510 is above the physical layer management entity (PLME) 506. The MLME 510 has a bandwidth manager (BM) 512 and a scheduling entity (SE) 514 as shown. A designated subnet bandwidth manager (DSBM) 516 is on the MLME 510. The DSBM 516 can communicate with the logical link control layer (LLC layer) 518, the MLME 510 and the SME 502. The LLC layer 518 is over the MAC layer 508 as shown. The LLC layer 518 includes a classification entity (CE) 520 and a flow control (FC) 522. Any of the various intermediate layers 524 can be on the LLC layer. Similarly, the application layer 526 can be above the middle layer 524. The MAC layer 508 has a hybrid coordination function (HCF) 528 as shown. The hybrid coordination function (HCF) 528 has a hybrid coordinator (HC) 530. The MAC layer 508 also has an extended distributed coordination function (EDCF) 532. HCF 528 and EDCF 532 are typically in QAP 160.

EDCF532 is based on the principle of “listen before speaking”, called carrier sense multiple access / collision avoidance (CSMA / CA) (can transmit frames after listening to channel for a random amount of time) Based on the protocol. CSMA / CA typically provides differentiated channel access to frames of various priorities as labeled by higher layers. EDCF due to the nature of distributed contention-based channel access along with the uncertainty of the wireless medium
532 cannot guarantee any rigid-type QoS. For example, in the transmission of layered video data over an unreliable wireless channel, if the capacity of the wireless medium falls below the minimum bit rate of the compressed data, some data packets are lost or discarded, and QoS Will be damaged by it. That is, the signaling achieved via TSPEC, which allows transmission of variable bit rate (VBR) video, can be applied when the wireless network is unable to adhere to the negotiated QoS due to errors. Do not take into account the point of time when you refuse to accept. Thus, even if one data packet is lost, TSPEC signaling cannot determine whether to reject the application. As a result, the scheduler (eg, SE 514) layer and part of the MAC layer (eg, MAC layer 508) are fully defined when data packets are lost and / or when the required QoS is not provided. It is not necessarily done. This means that various applications run unpredictably.

  The system and method according to the advantageous features of the present invention uses TSPEC with a flow control algorithm to achieve flexibility in the presence of a time-varying channel and to use a hierarchical representation to improve overall picture quality. Provide the mechanism. For example, referring to FIG. 6, an image / video encoder 602 receives video data 604 and receives a video bitstream and, in particular, a predetermined number of base layer (BL) packets 608 and a predetermined number of upper layers ( 1 illustrates an exemplary flow control algorithm 600 that is suitable for encoding into a multi-layer variable rate digital video bitstream comprising frames 606 with EL) packets 610. The BL packet 608 preferably has data essential for decoding, and the EL packet 610 preferably has data that improves its quality of video.

  As shown, the packets 608, 610 of each frame 606 are transmitted before those of the following frames. Further, packets 608, 610 per frame 606 must reach the receiver / decoder within a predetermined period of time (ie, frame decoding time) to be eligible for decoding and can be transmitted. The BL packet 608 is preferably transmitted before the EL packet 610 every frame 606, since the number of active packets 608, 610 varies at least in part due to variable channel conditions. Thus, it is more likely that an important BL packet 608 will arrive within a predetermined time period and that the communication channel will be maintained thereby.

  Once encoded, the data stream is sent to the flow control (FC) layer 612. Thereby, one or more packets of the video frame can be discarded as needed depending on the state of the wireless medium (eg, congested or not congested). For example, as shown, the FC layer 612 preferably discards one or more EL packets 610 if the wireless network becomes over congested. This includes various settings including setting an occupation value of a predetermined EL layer buffer and / or BL layer buffer (that is, a value suitable for ensuring effective communication in a wireless network with low reliability). It can be determined in any of the following ways. Thus, when a predetermined buffer occupancy value is exceeded, one or more EL layers are discarded as necessary to maintain the connection state. Alternatively, the EL packet 610 can be transmitted within a predetermined delay from the BL packet 608. The predetermined delay is preferably the entire delay to ensure that when an EL packet 610 is transmitted, it is guaranteed to be received by the receiver / decoder within a predetermined period for decoding. Less than end-to-end delay.

  The FC layer 612 sends the BL packet 608 and any remaining EL packets 610 to the scheduler (SE) 614. The scheduler (SE) 614 preferably schedules the transmission of packets 608, 610 to the MAC layer management entity (MLME) 616. Since SE 614 schedules / transmits a smaller number of packets depending on the communication channel conditions, the scheduler preferably does not discard any packets and / or rejects applications regardless of the communication channel conditions. It is not necessary to determine whether or not. The MLME 616 operates as a TSPEC interface as shown. A TSPEC with a modified minimum bit rate 618 is preferably capable of being transmitted over the air.

  While various aspects and / or features of the present invention have been clarified and described, the above examples and various aspects and features thereof are merely exemplary, and those skilled in the art will appreciate from the spirit and scope of the present invention. Many variations and / or modifications can be made without departing. All such variations and modifications are intended to be included within the scope of the present invention as set forth in the appended claims.

FIG. 2 schematically illustrates an exemplary prior art extended service set for a wireless local area network (WLAN). FIG. 2 schematically illustrates seven prior art open system interconnection (OSI) network hierarchies. FIG. 2 is a diagram schematically illustrating an exemplary prior art frame format for IEEE 802.11e QoS data. FIG. 2 schematically illustrates an exemplary prior art frame format for an IEEE 802.11e traffic specification element. FIG. 2 schematically illustrates an exemplary prior art architecture of a QoS radio station. FIG. 2 schematically illustrates an exemplary embodiment of a system and method according to the present invention.

Claims (19)

  A signaling method for transmitting layered video over a quality of service (QoS) enabled wireless local area network (WLAN), comprising a base layer (BL) packet and a higher layer (EL) packet A method comprising: providing a rate (VR) video stream; and discarding one or more EL packets using flow control if the wireless network becomes congested.   2. The method according to claim 1, further comprising the steps of: providing a scheduler; and scheduling the transmission of the BL packet and the remaining EL packets using the scheduler.   The method of claim 1 wherein the flow control determines when to discard one or more EL packets.   4. The method according to claim 3, wherein the flow control is configured to send one or more EL packets when a predetermined buffer occupancy of one or both of the BL packet and the EL packet exceeds a predetermined value. A method that works to discard.   4. The method of claim 3, wherein the flow control operates to discard one or more EL packets if the EL packet is not transmitted within a predetermined period.   6. The method according to claim 5, wherein the predetermined period is measured from the time when the BL packet is transmitted.   7. The method of claim 6, wherein the predetermined period is less than a predetermined end-to-end delay of a frame of interest that is available for decoding.   An encoder suitable for receiving video data and encoding into a video bitstream having a predetermined number of base layer (BL) packets and a predetermined number of upper layer (EL) packets; A system comprising a flow control layer capable of discarding one or more of the upper layer EL packets related to a stream according to the state of a wireless medium as needed, and a scheduler (SE) for scheduling the packets.   9. The system of claim 8, wherein the video stream is a multi-layer variable rate digital video bitstream.   9. The system of claim 8, wherein the encoded video stream is transmitted from the encoder to the flow control layer via a wireless transmitter.   9. The system according to claim 8, wherein the flow control layer discards the one or more upper layer EL packets when the wireless medium is congested.   9. The system according to claim 8, wherein the base layer BL packet and any remaining upper layer EL packets are sent from the flow control layer to the scheduler SE.   9. The system according to claim 8, wherein the scheduler SE schedules the predetermined number of base layer BL packets and lower layer EL packets less than the predetermined number and transmits them to a MAC layer management entity (MLME). System.   14. The system of claim 13, wherein the MAC layer management entity MLME operates as a TSPEC interface and is capable of transmitting TSPEC with a modified minimum bit rate over the air. A method of transmitting layered video over a quality of service (QoS) enabled wireless local area network (WLAN) comprising:
Generating a multilayer variable rate video bitstream having one or more base layer BL packets and one or more upper layer (EL) packets;
Transmitting the multilayer variable rate video bitstream to a flow control layer;
When the wireless network becomes congested, the multilayer variable rate video is discarded by discarding at least one of the one or more upper layer EL packets using the flow control layer. Modifying the bitstream.   16. The method of claim 15, wherein the modified multilayer variable rate video bitstream is transmitted to a scheduler (SE) that schedules the base layer BL packet and any remaining upper layer EL packets. A method of further comprising.   17. The method of claim 16, further comprising sending the scheduled packet to a MAC layer management entity (MLME) for wireless transmission.   [18] The method according to claim 17, wherein the MAC layer management entity MLME operates as a TSPEC interface and can wirelessly transmit a TSPEC with a modified minimum bit rate.   16. The method of claim 15, wherein the multi-layer variable rate video bitstream has a reduced minimum bit rate field to maintain a communication channel over an unreliable WLAN.

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