The present invention relates generally to wireless transmission systems, and relates more particularly to distributed channel time allocation and rate adaptation for multiple user video streaming.
Developing enhanced television systems is a significant consideration for consumer electronics manufacturers. In conventional television systems, a display device may be utilized to view program information received from a program source. The conventional display device is typically positioned in a stationary location because of restrictions imposed by various physical connections coupling the display device to input devices, output devices, and operating power. Other considerations such as display size and display weight may also significantly restrict viewer mobility in traditional television systems.
Portable television displays may advantageously provide viewers with additional flexibility when choosing an appropriate viewing location. For example, in a home environment, a portable television may readily be relocated to view programming at various remote locations throughout the home. A user may thus flexibly view television programming, even while performing other tasks in locations that are remote from a stationary display device.
Furthermore, a significant proliferation in the number of potential program sources (both analog and digital) available may benefit a system user by providing an abundance of program material for selective viewing. Examples of video sources include satellite and cable television transmission, terrestrial television broadcasts, digital video disks (DVD), video cassette recorders (VCR), digital video recorders (DVR), personal computers (PC) and the Internet. Video material may be available in either a live manner, for example from live broadcasts or live Internet video streaming, or in a stored manner, such as from video recorders or Internet downloads. In particular, an economical wireless audio/video transmission system for flexible home use may enable television viewers to significantly improve their television-viewing experience by facilitating portability while simultaneously providing an increased number of program source selections. The ease of installation of wireless home networks is another major benefit compared to wired home networks.
The evolution of digital data network technology and wireless digital transmission techniques may provide additional flexibility and increased quality to television systems in the home. However, current wireless data networks typically are not optimized for transmission of high quality video information.
High quality continuous media streams, such as video image streams, in their raw form often require high transmission rates, or bandwidth, for effective and/or timely transmission. In many cases, the cost and/or effort of providing the required transmission rate is prohibitive. This transmission rate problem is often solved by compression schemes that take advantage of the continuity in content to create highly packed data. Compression methods for audio and video such as based on ISO Motion Picture Experts Group (MPEG) standards, ITU standards and their variants are well known. With high resolution video, such as the resolutions of 720p, 1080i, or 1080p, used in high definition television (HDTV), the data transmission rate of such a video image stream will be very high even after compression.
It may be difficult to transmit continuous media in networks with a limited bandwidth or capacity. For example, in a local area network with multiple receiving/output devices, such a network will often have a limited bandwidth or capacity, and hence be physically and/or logistically incapable of simultaneously supporting multiple receiving/output devices. Furthermore, the available bandwidth of wireless interconnections and networks often varies over time and is unpredictable due to several factors.
Transmission of compressed media data over such networks is difficult, because a high bandwidth is required continuously, and because of the stringent delay constraints associated with continuous media streams. Degradation of the channel condition may result in data packets being lost or delayed, leading to distortions or interruptions of the media presentation.
In some cases for video an ad hoc wireless network is a collection of wireless nodes which communicate with each other without the assistance of fixed infrastructure. In some cases, these wireless nodes may be configured as a wireless mesh network. Each node may be a source, a destination, and/or a relay for traffic. Wireless links between nodes are established when needed for transmission of data. Since the installation of such a network is fast and flexible because the nodes may be located at suitable locations and merely turned on, it is useful to support real-time media streaming over such an ad hoc network. However, in such ad hoc networks the limited power resources and bandwidth limitations of the wireless nodes, combined with the demanding rate and delay requirements of video streaming, impose limitations that are not typical of conventional data networking. In particular, rate allocation, scheduling, and routing of the video packets should be done in such a manner for efficient utilization of the network resources without overwhelming any individual wireless link.
When multiple video streams are present in the network, they share and compete for the common resources such as transmission power and media access. The shared wireless channel is subject to interference from other transmitters, multi-path fading and shadowing, causing fluctuations in link capacities and transmission errors. Also, the traffic patterns of compressed media streams typically change over time due to content variations and dynamic user behavior, the received media quality may be degraded due to packet losses, and error propagation may occur in the compressed bit stream. Further, media streaming applications usually have high data rate and stringent latency requirements, which is at odds with the limited bandwidth recourses in a wireless network. Rate allocation among various media streams serves the purpose of resource allocation among the video streams. In general, a transmitter at a high video source rate utilizes more network resources and achieves better quality of the transmitted video. The rate allocated for a particular video stream determines the distortion of that video stream. Moreover, the rate-distortion tradeoff for different video streams are usually different, hence it is preferable to allocate rates to the video streams in a manner that considers this tradeoff. In general, the rate allocation technique should achieve a fair and efficient resource allocation among the video streams using the ad hoc network. It is also desirable to have a distributed technique so that the computational burden is shared among the participating nodes to reduce the computations requirements of any particular node.
For multi-user video streaming over ad hoc wireless networks, one technique is to use a centralized scheme for minimizing the total video distortion under a total rate constraint for the network. While such a centralized approach suits well for some applications, such as surveillance video with a common receiver, it introduces significant additional overhead due to the need for collection of information at the central decision node as well as the need to communicate the decisions taken at the central node to all other nodes.
It is desirable to have distributed channel time allocation that adapts the rate for multiple users of a wireless network.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.
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