Adaptive Video Coding over a Wireless Channel

The main purpose of this project is to study the effect of video quality when it is transmitted over the wireless channel and design efficient coding schemes which will be best suited for that environment. Due to the dynamic nature of the channel and the uncertainty associated with the user's mobility, No constant bit-rate encoding will be able to survive the dynamism offered by the hostile environment. Hence, we propose an adaptive scheme which will be more robust to the varying channel conditions and will take into consideration the channel state and will adaptively change the encoding parameters without disrupting the on-going session.

We propose to use the most recent information available about the channel to encode the incoming video stream. The decoder at the receiver side, apart from decoding, will also monitor the signal strength and the bit error rate as experienced by the packets. These parameters will be captured and passed on to the encoder using a feed-back control mechanism.

The parameters for the feedback are the subject of study. The feedback from the network (channel) will help us make wise decisions and help us predict the channel in near future. The translation of the feedback parameters to the encoding parameters will be done with the help of a transfer function. The design of the transfer function and its response time is an important issue. If the channel recovers before the response time, then it does not help. It will be useful if the duration of bad phase is large enough compared to the response time of the feedback system.

The idea is to employ dynamically changing network policies on the stream. We can simulate different traffic load patterns by artificially generating streams that are simple noise generators. The idea is to find out how the QoS changes in response to this noise. Obviously to demonstrate this fault-tolerance behavior, the QoS and path need to be pre-negotiated. The experiment will tell us the response time for the value adaptation.

Scalable coding schemes help in playing back a video sequence at different resolutions. We propose to use Discrete Wavelet transform (DWT) for the multi-resolution signal decomposition. The decomposition of the frames into frequency subbands will depend on the feedback control system. The encoder will decide the number of subbands to be encoded and transmitted. To our knowledge, there has been no real-time adaptive implementation of wavelet-based video compression algorithm on a DSP board. This proposal aims at opening up a new avenue for future work on DSP-based implementation of wireless video-communication products in the future.

People

• Mainak Chatterjee
• Sourav Pal