Television by the bit

The various types of advanced television (ATV) are defined, and the most advanced type, high-definition TV (HDTV), is discussed. The present status of HDTV development in the US, Japan, and Europe is examined. Signal processing requirements for HDTV are briefly considered, and the benefits of and prospects for all-digital HDTV are explored. Video compression techniques, implementation issues, and the future of HDTV are also discussed     

Error control using retransmission schemes in multicast transportprotocols for real-time media

We analyze different retransmission (ARQ) schemes for error control in multicast protocols geared toward real-time, multimedia applications. We discuss why retransmission schemes are not inappropriate for such applications, but in fact can be quite effective. We present a quantitative analysis of such schemes, as well as simulation results, taking into account four different parameters (and not just the source throughput): (1) the probability of dropping a packet due to limited time for retransmissions; (2) the average time required to deliver a packet correctly to end receivers; (3) the number of times a packet will be retransmitted; and (4) the cost to the network, in terms of packet duplications, of retransmitting a packet. We reach the counter-intuitive conclusion that the optimum scheme, in terms of all four of the above parameters, in the most general scenarios (where several hosts with widely varying propagation delays and `quality of connections' are participating in the session) is to immediately retransmit packets-preferably multicast-upon reception of a NACK from any receiver. We also demonstrate, again through quantitative analysis, the circumstances under which it would be beneficial (as well as those under which it would be counter-productive) to multicast control messages in the hope of suppressing duplicates and preventing the source from being overwhelmed by control messages     

Subsecond voltammetric separation between dopamine and serotonin in the presence of ascorbate

Although voltammetry has proved an important tool for unraveling the dynamics of specific neurotransmitter molecules during the past decade, it has been very difficult to monitor more than one neurotransmitter simultaneously. In this work, we present a voltammetric methodology that allows discrimination between dopamine and serotonin, two important neurotransmitter molecules with very similar electrochemical properties, in the presence of high concentrations of ascorbate. We combined the application of a novel large-amplitude/high-frequency voltage excitation with signal processing techniques valid for the analysis of nonstationary and nonlinear phenomena. This allows us to minimize the contribution from capacitance and preserve the faradaic features of the voltammetric response providing us with excellent voltammetric detail. Using appropriate voltage excitation parameters and defining specific regions in the voltage space, so-called voltage windows, we can measure the concentrations of dopamine and serotonin separately or independently in mixed solutions even in the presence of high concentrations of ascorbate. Because of the enhanced voltammetric detail of this new technique, it is also possible to explore effects attributed to interfacial phenomena such as adsorption/desorption and electrode fouling.     

Digital television

It is now recognized worldwide that all television services, including HDTV, will eventually become digital, but there is wide disagreement about the optimum timing for transforming existing analog systems. A major driving force is the ongoing partial merging of television and digital computers in interactive multimedia services involving digital television and applications in areas like information (news), education, medical, entertainment, etc. A major target is to maximize interoperability of video services at all levels, including various resolutions, different transmission and storage mechanisms, as well as bit rates. This paper provides an overview of the current status in digital television, techniques used, future prospects, and research areas that need to be investigated. The maturity of compression techniques needed for digital video storage and transmission, and the establishment of international standards for digital television representation, like MPEG-2, have greatly contributed in this transformation. Recent developments are mentioned, including the American “Grand Alliance” FCC effort for digital terrestrial HDTV broadcasting, and also other efforts for digital television by cable and DBS. The concept of hierarchical multiresolution coding is also explained, and some of its techniques are briefly described     

Subpixel edge localization and the interpolation of still images

In this paper, we present a nonlinear interpolation scheme for still image resolution enhancement. The algorithm is based on a source model emphasizing the visual integrity of detected edges and incorporates a novel edge fitting operator that has been developed for this application. A small neighborhood about each pixel in the low-resolution image is first mapped to a best-fit continuous space step edge. The bilevel approximation serves as a local template on which the higher resolution sampling grid can then be superimposed (where disputed values in regions of local window overlap are averaged to smooth errors). The result is an image of increased resolution with noticeably sharper edges and, in all tried cases, lower mean-squared reconstruction error than that produced by linear techniques.     

Architecture and algorithms of the Xphone multimedia communication system

We describe the architecture and the algorithms used in Columbia University'sXphone multimedia communication system. The system assumes a best-effort operating system and network and provides facilities for call management, intra-application scheduling for the support of continuous data flow and integration with the windowing system, and synchronized video/audio acquisition/playback (locally or across a network) with minimized and bounded end-to-end delay. An algorithm based on time-stamps and device-state information is used for synchronization. The effects of jitter (delay variation) are mitigated with silence detection; the end-to-end delay is kept bounded by a restart mechanism. Finally, for live video sources, we describe a source bit-rate adaptation algorithm that maximizes the video image quality to the available network bandwidth and video display window size.     

Performance models of statistical multiplexing in packet videocommunications

Models and results are presented that assess the performance of statistical multiplexing of independent video sources. Presented results indicate that the probability of buffering (or delaying) video data beyond an acceptable limit drops dramatically as the number of multiplexed sources increases beyond one. This demonstrates that statistical or asynchronous time-division multiplexing (TDM) can efficiently absorb temporal variations of the bit rate of individual sources without the significant variations in reception quality exhibited by multimode videocoders for synchronous TDM or circuit-switched transmission. Two source models are presented. The first model is an autoregressive continuous-state, discrete-time Markov process, which was used to generate source data in simulation experiments. The second model is a discrete-state, continuous-time Markov process that was used in deriving a fluid-flow queuing analysis. The presented study shows that both models generated consistent numerical results in terms of queuing performance