We consider rate optimization in multicast systems that use several multicast trees on a communication network. The network is shared between different applications. For that reason, we model the available bandwidth for multicast as stochastic. For specific network topologies, we show that the multicast rate optimization problem is equivalent to the optimization of scalar quantization. We use results from rate-distortion theory to provide a bound on the achievable performance for the multicast rate optimization problem. A large number of receivers makes the possibility of adaptation to changing network conditions desirable in a practical system. To this end, we derive an analytical solution to the problem that is asymptotically optimal in the number of multicast trees. We derive local optimality conditions, which we use to describe a general class of iterative algorithms that give locally optimal solutions to the problem. Simulation results are provided for the multicast of an i.i.d. Gaussian process, an i.i.d. Laplacian process, and a video source.

In live video communication, the quality of the video that is encoded on a mobile device is more often than not constrained by the available computational resources. We address this problem by allowing the encoder to “outsource” the encoding complexity to the decoder through the use of feedback, under a sum-rate constraint comprising the weighted sum of the forward and feedback rates. Analysis of such a complexity-outsourced framework using an analytically tractable video model reveals that the feedback rate should be optimally adapted to the video motion characteristics. Application of our framework to real-world video sequences reveals the efficacy of our proposed architecture, with experimental results validating that substantial gains in PSNR are achievable over state-of-the-art fast-search algorithms at a comparable level of complexity. These gains are significant even for mobile live video communication applications over the Internet.

We investigate the design of a frame-bufferless and low-latency video communication system, where the encoder has no access to any previous frames and only one use of feedback communication from the decoder to the encoder is allowed in encoding each frame. This strict requirement on encoder complexity and system latency is of critical importance in designing low complexity realtime video communication systems, where the encoder is limited in storage and computing resources and the use of the feedback channel must not incur accumulated receiver playback delay. We propose a simple online statistical model that captures the time-varying video process and develop a general framework that explores how to best utilize the feedback and distributed source coding mechanisms to minimize the overall communication rate. Our analysis and experimental results validate the efficiency of the proposed system and highlight its potential in practical system design.

We consider the optimization of multicast over packet-switched communication networks with a non-zero packet-loss probability. For the system setup consisting of a number of multiple-description coders, we jointly optimize these coders. We propose an analytic so-lution, asymptotically optimal in the number of multiple-description coders. The analytic solution allows for fast system adaptation to changing network conditions. A locally optimal optimization algo-rithm that is useful when the number of multicast groups is small is derived. Simulations show that the utilization of the analytic solution incurs a low overhead on the performance when compared to the locally optimal solution, even for a small number of multiple-description coders. Index Terms — Multicast, multiple-description coding, opti-mization, packet-loss

We introduce a method to improve performance of multiple-description coding based on legacy video coders with pre-and postprocessing. The pre-and post-processing setup is general, making the method applicable to most legacy coders. For the case of two coders, a relative displacement of the intra-coding mode between the coders is shown to give improved robustness to packet loss. The optimal displacement of the intra-coding mode is found analytically, using a distortion minimization formulation where two independent Gilbert channels are assumed. The analytical results are confirmed by simulations. Tests with an H.263 coder show significant improvement in YPSNR over equivalent systems with no relative displacement of the intra-coding operation.