Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from U-Z

Video Delivery Over Wireless Multi-Hop Networks

layer control layers protocol

Qian Zhang
Microsoft Research Asia, Beijing, China

Definition : A wireless multi-hop network is a collection of wireless nodes that dynamically form a temporary network without an infrastructure.

A multi-hop network is dynamically self-organized and self configured, with the nodes in the network automatically establishing and maintaining mesh connectivity among themselves. This feature brings many advantages to multi-hop networks such as low upfront cost, easy network maintenance, robustness, and reliable service coverage. With the increase in the bandwidth of wireless channels, and in the computing power of devices, video applications are expected to become available in wireless multi hop networks in a near future. However, limited network resource, severe interference/ contention among neighbor traffic, dynamic changing route, lack of QoS support, direct coupling between the physical layer and the upper layers, etc. pose many challenges for supporting video communication over wireless multi- hop networks.

Target at the above challenges, it is essential to improve the quality for multimedia delivery over wireless multi-hop networks from different aspects. More specifically,

  • To handle the impact of channel error to compressed media, it is important to have the efficient and resilient video coding and protection solutions.

Many research works have been there trying to address the best tradeoff between error resilience and coding efficiency under different conditions. Considering wireless multi-hop network can establish more than one path between a source and a destination given their mesh topology, recently people start thinking about leveraging multi-path to further improve the efficiency. Feedback Based Reference Picture Selection (RPS), Layered Coding with Selective ARQ, and Multiple Description Coding (MDC) are three representative schemes along this direction.

  • Target at dealing with the dynamic changing network condition and utilizing the uniqueness of multi-hop networks (e.g., multiple paths available due to the mesh topology), it is essential to design new network and transport protocols.

The mesh topology of multi-hop networks provides the existence of multiple routes between two endpoints which can be utilized to perform multipath streaming to better support real time multimedia applications. The two important issues need to be addressed are listed as follows. Firstly, packet losses due to different causes (i.e., congestion, channel error, and route change/break) should be differentiated so that congestion control and error control can be performed properly. Secondly, streaming protocols need to choose multiple maximally disjointed paths to achieve good streaming quality. A number of approaches including Ad Hoc TCP Friendly Rate Control (ADTFRC), Multi-flow Realtime Transport Protocol (MRTP), Robust Multipath Source Routing Protocol (RMSRP), and Ad hoc Multipath sTreaming Protocol (AMTP) are proposed to enable multimedia streaming over multiple paths in multi-hop networks.

  • To provide QoS support for multimedia delivery, research studies related to link layer, including scheduling and enhanced MAC are also quite important.

Due to the existence of hidden terminal and the lack of centralized control, it is very challenge to have QoS support for multi-hop wireless networks. Several distributed scheduling algorithms, such as congestion-distortion optimized scheduling (CoDiO), opportunistic packet scheduling and auto rate (OSAR), distributed link scheduling multiple access (D-LSMA), are proposed to extend 802.11 MAC so that permit nodes to reserve periodic time slices for real-time flows. Do not change the existing 802.11 MAC, SoftMAC employs “coarse-grained” control mechanisms (e.g., distributed admission control and rate regulation) to coordinate and regulate network load and packet transmission of both RT and BE traffic among neighboring nodes in a distributed manner.

  • Finally, to improve the overall wireless network performance, cross-layer approaches that jointly consider different layers, including multimedia application, routing and transport protocol, link layer scheduling, and physical layer power control are drawing great attention.

The cross-layer network design of video streaming over multi-hop wireless networks is still in its infancy. Most of the recent research considers only a subset of layers of the protocol stack. A more general framework is proposed recently, which encompasses the entire protocol stack. One thing that needs to be paid much attention is that a cross-layer approach can significantly increase the design complexity. Keeping some form of separation, while allowing layers to actively interact, appears a good compromise for enabling interaction between layers without eliminating the layering principle. Moreover, cross-layer design does not necessarily mean that all the layers should interact together. How to identify the layers, that can generate the most significant gains by interacting together present important areas of future research.

Enabling multimedia transport over wireless multi-hop networks is an exciting yet challenging task. Deeper studies are needed for each the above direction.

Video Inpainting [next] [back] Video Databases - Video data models, Video Extraction, Video Query Language, Video Index Structures

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

almost 7 years ago

nice explanation