Channel Modeling for a Wireless Transmission System

Air Force Research Laboratory, Rome, New York

Thursday, April 01 2010

The resulting system provides video transmission over severely impaired wireless links within airborne networks.

A wireless transmission system provides high-quality video transmission over severely impaired wireless links between nodes that are connected within airborne networks. The target bit rate for the proposed video communication can be in the range between 24 Kbps and 384 Kbps with relatively high visual quality. However, the system may operate at extreme low bit rates down to 10 Kbps and at high bit rates up to 1.5 Mbps. To accommodate the large range of the data rate for heterogeneous wireless links and devices, the H.264 SVC standard for video coding and decoding was adopted.

To overcome the adversity of the video transmission in tactical airborne wireless networks with various constraints in terms of bandwidth, channel impairments, bursty errors, and packet loss, and media access control for battery operated end users, an end-to-end design principle embraces the joint source and channel coding as the key strategy, and the channel estimation and feedback as the means of providing adaptation. Various building blocks of the proposed system and the relationship between these building blocks are shown in the figure.

The proposed system can be divided into three major functionalities: (1) video source encoding and decoding, (2) error correction channel encoding and decoding, and (3) channel modeling and estimation. Since it has been well known that the joint source and channel coding is able to significantly improve the end-to-end quality of service for video transmission, these functional components can no longer be treated separately. This is evident from the figure that many of these building blocks are interconnected to facilitate joint design of the end-to-end system.

• Video Encoding and Decoding. H.264 SVC standard video coding was used as a base for video encoding and decoding. Such a selection of standard video codec will enable the smooth exchange of motion imagery among different DoD agencies. In addition to this important consideration, H.264 SVC video encoding and decoding schemes are inherently able to facilitate the required error control strategies, including error resilience tools, data partition for unequal error protection, and error concealment. Significantly improved results have been obtained by joint source and channel coding based on MPEG-4 codec for video delivery over both packet loss network and wireless fading channels.
• Channel Encoding and Decoding. The main reason for the incorporation of channel encoding and decoding is that the communication links between platform nodes within airborne networks can be severely impaired. The embedded error resilience in H.264 SVC video codec is inadequate to overcome such channel impairment. Additional error control strategies need to be implemented. A combination of error control codes was selected for the proposed system in order to combat the bursty error in the wireless links, as well as the packet loss error due to networking manageing management. In combination with intelligent interleaving, and the error-resilient MPEG-4 tools, a joint design of channel coding and source coding has been shown to achieve high end-to-end quality of service for composite channel impairments with both packet loss and burst fading errors.


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