5685846
Advances in channel-adaptive video streaming
Despite the well-known challenges of variations in throughput, delay, and packet loss over the Internet, video streaming has experienced phenomenal growth, owing to the extensive research in video coding and transmission. In this paper, we review several recent advances for channel-adaptive video streaming that, we believe, will benefit the design of video streaming systems in the future. Employed in different components of the system, these techniques have the common objective of providing efficient, robust, scalable, and low-latency streaming video. Firstly, by allowing the client to control the rate at which it consumes data, adaptive media playout can be used to reduce receiver buffering and therefore average latency, and provide limited rate scalability. Secondly, rate-distortion optimized packet scheduling, a transport technique, provides a flexible framework to determine the best packet to send, given the channel behaviors, the packets' deadlines, their transmission histories, the distortion reduction associated with sending each packet, and the interpacket dependencies. Thirdly, at the source encoder, channel-adaptive packet-dependency control can greatly improve the error resilience of streaming video and reduce latency. Finally, we address the specific additional challenges for wireless video streaming. We consider three architectures for wireless video and discuss the utility of the reviewed techniques for each architecture. Copyright © 2002 John Wiley & Sons, Ltd.
17534707
Upfront intra-refresh decision for low-complexity wireless video telephony
An adaptive intra-refresh (IR) technique is proposed for low-complexity video encoding on resource-constrained wireless platforms. The IR decision is made upfront without requiring any pre-encoding, which significantly reduces the complexity and power consumption in real-time communication. To allow upfront mode decision, a novel closed-form solution is provided requiring no algorithmic iteration or exhaustive searches. The IR scheme adapts to multiple factors including the content texture information, the frame-to-frame pixel-value variation, and the estimated channel loss probability. The macroblock-based refresh can be performed using various patterns (i.e., cyclic, random etc.). Experimental results demonstrate superior performance of the adaptive scheme over fixed schemes at all channel loss rates
6443463
Prescient R-D optimized packet dependency management for low-latency video streaming
An improved, prescient, scheme to deliver preencoded video streams at very low latency is presented. We dynamically manage the prediction dependency for a group of packets using a rate-distortion (R-D) optimization framework that adapts to the channel, so that the expected end-to-end distortion is minimized under a given rate constraint. In our system, the R-D characteristics of each prediction mode are precomputed at compression time and stored in an R-D preamble along with the multiple compressed versions of the stream. The distortion in the preamble is estimated using an accurate loss-distortion model, and the optimal prediction modes are computed with an iterative descent algorithm. Complexity is reduced at streaming time by using the preamble to compute the optimal modes instead of actually compressing the video. Experiments demonstrate that the proposed prescient scheme provides significant performance gains over simple intra-insertion, and consistent bitrate savings compared to the greedy scheme.
34209487
Advances in channel-adaptive video streaming
We review recent advances in channel-adaptive video streaming. Adaptive media playout at the client can be used to reduce receiver buffering and therefore average latency, and provide a limited rate scalability. Rate-distortion optimized packet scheduling determines the best packet to send given the distortion reduction associated with sending that packet, interpacket dependencies, and the success of past transmissions. Channel-adaptive packet dependency control can greatly improve the error-robustness of streaming video and reduce or eliminate the need for packet retransmissions. Finally we consider three architectures for wireless video streaming and discuss the utility of the discussed techniques for each architecture.
7289490
Low-latency video transmission over lossy packet networks using rate-distortion optimized reference picture selection
Today's Internet video streaming systems employ buffering and multiple retransmissions to guarantee the correct reception of each packet, which leads to high latency in media delivery. In this work, a novel scheme of dynamic management of the dependency across packets is proposed using optimal reference picture selection at the frame level that adapts to the channel. The optimal selection of the reference picture is achieved with a rate-distortion framework, which minimizes the expected end-to-end distortion given a rate constraint. The expected distortion is calculated based on an accurate binary tree modeling with the effects of channel loss and error concealment taken into account. Experiments demonstrate that the proposed :scheme provides significant performance gains over a simple INTRA-insertion scheme. The increased error-resilience eliminates the need of retransmission, which makes it possible to reduce the latency from 10-15 seconds to a few hundred milliseconds, with similar video quality maintained.
14328757
Adaptive playout scheduling and loss concealment for voice communication over IP networks
The quality of service limitation of today's Internet is a major challenge for real-time voice communications. Excessive delay, packet loss, and high delay jitter all impair the communication quality. A new receiver-based playout scheduling scheme is proposed to improve the tradeoff between buffering delay and late loss for real-time voice communication over IP networks. In this scheme the network delay is estimated from past statistics and the playout time of the voice packets is adaptively adjusted. In contrast to previous work, the adjustment is not only performed between talkspurts, but also within talkspurts in a highly dynamic way. Proper reconstruction of continuous playout speech is achieved by scaling individual voice packets using a time-scale modification technique based on the Waveform Similarity Overlap-Add (WSOLA) algorithm. Results of subjective listening tests show that this operation does not impair audio quality, since the adaptation process requires infrequent scaling of the voice packets and low playout jitter is perceptually tolerable. The same time-scale modification technique is also used to conceal packet loss at very low delay, i.e., one packet time. Simulation results based on Internet measurements show that the tradeoff between buffering delay and late loss can be improved significantly. The overall audio quality is investigated based on subjective listening tests, showing typical gains of 1 on a 5-point scale of the Mean Opinion Score.
1136997
Cooperative Relay Broadcast Channels
The capacity regions are investigated for two relay broadcast channels (RBCs), where relay links are incorporated into two-user broadcast channels to support user cooperation. In the first channel, the partially cooperative RBC, only one user in the system acts as a relay. An achievable rate region is derived based on the relay using the decode-and-forward scheme. An outer bound on the capacity region is derived and is shown to be tighter than the cut-set bound. For the special case where the partially cooperative RBC is degraded, the achievable rate region is shown to be the capacity region. Two Gaussian cases of the partially cooperative RBC are studied. For the system where the additive white Gaussian noise (AWGN) term at one receiver is a degraded version of the other, which we refer to as the D-AWGN partially cooperative RBC, the capacity region is established. For the system where the AWGN term at one receiver is independent of the other, which we refer to as the AWGN partially cooperative RBC, inner and outer bounds on the capacity region are derived and are shown to be close. Furthermore, it is shown that feedback does not increase the capacity region for the degraded partially cooperative RBC, but that it improves the capacity region for the nondegraded version. In particular, feedback improves the capacity region for the AWGN partially cooperative RBC. In the second channel model being studied in the paper, the fully cooperative RBC, both users can act as relay nodes. All the results for the partially cooperative RBC are correspondingly generalized to the fully cooperative RBC. In particular, capacity regions are established for the degraded and D-AWGN fully cooperative RBCs. The capacity region is also established for the fully cooperative RBC with feedback. It is further shown that the AWGN fully cooperative RBC has a larger achievable rate region than its partially cooperative counterpart. The results illustrate that relaying and user cooperation are powerful techniques for improving the capacity of broadcast channels
18261713
Differential and trajectory methods for time course gene expression data
MOTIVATION
The issue of high dimensionality in microarray data has been, and remains, a hot topic in statistical and computational analysis. Efficient gene filtering and differentiation approaches can reduce the dimensions of data, help to remove redundant genes and noises, and highlight the most relevant genes that are major players in the development of certain diseases or the effect of drug treatment. The purpose of this study is to investigate the efficiency of parametric (including Bayesian and non-Bayesian, linear and non-linear), non-parametric and semi-parametric gene filtering methods through the application of time course microarray data from multiple sclerosis patients being treated with interferon-beta-1a. The analysis of variance with bootstrapping (parametric), class dispersion (semi-parametric) and Pareto (non-parametric) with permutation methods are presented and compared for filtering and finding differentially expressed genes. The Bayesian linear correlated model, the Bayesian non-linear model the and non-Bayesian mixed effects model with bootstrap were also developed to characterize the differential expression patterns. Furthermore, trajectory-clustering approaches were developed in order to investigate the dynamic patterns and inter-dependency of drug treatment effects on gene expression.


RESULTS
Results show that the presented methods performed significant differently but all were adequate in capturing a small number of the potentially relevant genes to the disease. The parametric method, such as the mixed model and two Bayesian approaches proved to be more conservative. This may because these methods are based on overall variation in expression across all time points. The semi-parametric (class dispersion) and non-parametric (Pareto) methods were appropriate in capturing variation in expression from time point to time point, thereby making them more suitable for investigating significant monotonic changes and trajectories of changes in gene expressions in time course microarray data. Also, the non-linear Bayesian model proved to be less conservative than linear Bayesian correlated growth models to filter out the redundant genes, although the linear model showed better fit than non-linear model (smaller DIC). We also report the trajectories of significant genes-since we have been able to isolate trajectories of genes whose regulations appear to be inter-dependent.
2252341
Capacity of noncoherent time-selective Rayleigh-fading channels
The capacity of noncoherent time-selective Rayleigh-fading channels is studied under various models for the variations in time. The study includes both single-input and single-output (SISO) and multiple-input and multiple-output (MIMO) systems. A block-fading model is first considered where the channel changes correlatively over each block period of length T, and independently across blocks. The predictability of the channel is characterized through the rank Q of the correlation matrix of the vector of channel gains in each block. This model includes, as special cases, the standard block-fading model where the channel remains constant over block periods (Q=1), and models where the fading process has finite differential entropy rate (Q=T). The capacity is initially studied for long block lengths and some straightforward but interesting asymptotes are established. For the case where Q is kept fixed as T/spl rarr//spl infin/, it is shown that the noncoherent capacity converges to the coherent capacity. For the case where both T,Q/spl rarr//spl infin/, with Q/T being held constant, a bound on the capacity loss due to channel unpredictability is established. The more interesting scenario of large signal-to-noise ratio (SNR) is then explored in detail. For SISO systems, useful upper and lower bounds on the large SNR asymptotic capacity are derived, and it is shown that the capacity grows logarithmically with SNR with a slope of T-Q/spl rarr/T, for Q<T. Next, in order to facilitate the analysis of MIMO systems, the rank-Q block-fading model is specialized to the case where each T-symbol block consists of Q subblocks of length L, with the channel remaining constant over each subblock and changing correlatively across subblocks. For this model, it is shown that the log SNR growth behavior of the capacity is the same as that of the standard block-fading model with block length L. Finally, the SISO and MIMO channel models are generalized to allow the fading process to be correlated across blocks in a stationary and ergodic manner. It is shown that the log SNR growth behavior of the capacity is not affected by the correlation across blocks.
41985683
Constraint Satisfaction In "Conscious" Software Agents--A Practical Application
ABSTRACT The U.S. Navy has been trying for many years to automate its personnel assignment process. Periodic assignment of personnel to new jobs is mandatory according to Navy policy. Though various software systems are used regularly, the process is mainly done manually and sequentially by Navy personnel called detailers. This paper is a case study in applying cognitive theories implemented via new AI techniques to produce flexible adaptive human-like software. In it we present a sketch of an intelligent distribution agent that aims to largely automate the detailer's tasks. In particular, we look inside its constraint satisfaction, which is mainly responsible for satisfying the requirements of the Navy's policies, the command's needs, and the sailor's preferences in order to achieve “satisfactory” job assignments, according to ever-evolving Navy standards.
38500613
On the Feedback Vertex Set Problem in Permutation Graphs
Abstract Brandstadt and Kratsch (1987) presented an O( n 6 ) time algorithm for the minimum weight feedback vertex set problem in a permutation graph of n vertices and m edges. This result was recently improved to O( n.m.m ) by Brandstat (1993), where m is the number of edges in the complement of G . In this paper, we employ a different dynamic programming scheme to reduce the time complexity to O( nm ) for this problem in permutation graphs.