6153081
Zero-Error Capacity for Models with Memory and the Enlightened Dictator Channel
Summary form only given. We present a general class of "combinatorial" 0-error capacity problems with the "memory" covering known and many new cases. This class can be incorporated into a model of channels with memory. W analyse a seemingly basic channel in this class, which we call the "dictator channel". Clearly, a dictator always follows his own opinion. However, we speak of an enlightened dictator, if he responds to the unanimous vote of the people against his opinion to the degree, in this case he reaches a decision by coin tossing.
43476378
Partial converse for a relay channel
A special case of the general discrete memoryless relay channel is studied. This channel consists of an input x, a relay output z, a channel output y, and a noiseless channel of capacity C/sub r/ allowing the relay sender to send additional information to the decoder. The channel is described by a collection of distributions (p(y, z mod x)). The decoder uses the channel output y and a function f(z) of the relay output at a rate no greater than C/sub r/ to recover the message. Some results on the capacity of the channel are obtained. >
15006226
Bounds on the sizes of constant weight covering codes
Motivated by applications in universal data compression algorithms we study the problem of bounds on the sizes of constant weight covering codes. We are concerned with the minimal sizes of codes of lengthn and constant weightu such that every word of lengthn and weightv is within Hamming distanced from a codeword. In addition to a brief summary of part of the relevant literature, we also give new results on upper and lower bounds to these sizes. We pay particular attention to the asymptotic covering density of these codes. We include tables of the bounds on the sizes of these codes both for small values ofn and for the asymptotic behavior. A comparison with techniques for attaining bounds for packing codes is also given. Some new combinatorial questions are also arising from the techniques.
32850524
Linear inequalities for covering codes: Part I: Pair covering inequalities
The lower bounds on K(n,R), minimum number of codewords of any binary code of length n, and covering radius R are improved. A new technique combining the Hamming association scheme and the results of a classic problem of covering pairs by k-tuples is introduced. The new lower bounds are obtained by studying various linear inequalities satisfied by covering codes, and such an inequality is derived. The lower bounds for K(n,R) are studied for some special values of n and R, which serve as examples showing how the methods developed are applied to concrete cases. >
32960689
On Maximal Shadows of Members in Left-compressed Sets
Whereas Stanley, Proctor and others studied Sperner properties of the poset L(k,m) we consider shadows of left-compressed sets and derive asymptotic bounds on their sizes.
19004655
Identification via compressed data
A new coding problem is introduced for a correlated source (X/sup n/,Y/sup n/)/sub n=1//sup /spl infin//. The observer of X/sup n/ can transmit data depending on X/sup n/ at a prescribed rate R. Based on these data the observer of Y/sup n/ tries to identify whether for some distortion measure /spl rho/ (like the Hamming distance) n/sup -1/ /spl rho/(X/sup n/,Y/sup n/)/spl les/d, a prescribed fidelity criterion. We investigate as functions of R and d the exponents of two error probabilities, the probabilities for misacceptance, and the probabilities for misrejection. In the case where X/sup n/ and Y/sup n/ are independent, we completely characterize the achievable region for the rate R and the exponents of two error probabilities; in the case where X/sup n/ and Y/sup n/ are correlated, we get some interesting partial results for the achievable region. During the process, we develop a new method for proving converses, which is called "the inherently typical subset lemma". This new method goes considerably beyond the "entropy characterization" the "image size characterization," and its extensions. It is conceivable that this new method has a strong impact on multiuser information theory.
14282413
Distance-adaptive update protocols for scalable shared-memory multiprocessors
While update protocols generally induce lower miss rates than invalidate protocols, they tend to generate much traffic. This is one of the reasons why they are considered less cost-effectively scalable than invalidate protocols and, as a result, are avoided in most existing designs of scalable shared-memory multiprocessors. However, given the increasing relative cost of cache misses, update protocols are becoming more worthy of exploration. In this paper, we present a model of sharing that is key to investigating the performance of optimized update protocols: the update distance model. The model gives insight into the update patterns that optimized protocols need to handle. Using this model, we design a new family of protocols that we call distance-adaptive protocols. In these schemes, the directory records the update patterns observed and then uses them to selectively send updates and invalidations to processors. As a result, traffic and miss rates are kept low. We present an implementation of these protocols based on a dynamic pointer scheme. A performance comparison between one of these protocols and efficient invalidate and delayed competitive-update protocols over five applications shows that the new protocol decreases the execution time by an average of 15% and 10% respectively.
29297629
An Application of Fuzzy Cluster analysis to Matchmaking in Middle Agents
2128570
Peer-to-peer based multimedia distribution service
Recently, there are many research interests in providing efficient and scalable multimedia distribution service. However, stringent quality-of-service (QoS) requirements for media distribution, as well as dynamically changing and heterogeneous network capacity in today's best effort Internet, bring many challenges. In this paper, we introduce a novel framework for multimedia distribution service based on peer-to-peer (P2P) networks. A topology-aware overlay is proposed in which hosts self-organize into groups. End hosts within the same group have similar network conditions and can easily collaborate with each other to achieve QoS awareness. In order to improve media delivery quality and provide high service availability, we further propose two distributed heuristic replication strategies, intergroup replication and intragroup replication, based on this topology-aware overlay. Specifically, intergroup replication is aimed to improve the efficiency of media content delivery between the group where a request is issued and the group where the content is stored. Also, intragroup replication is targeted at improving the availability of the content. Extensive simulation results show that the latency in our proposed architecture is 20% less than that of the FreeNet and 50% less than that of the randomly replication system. Simulation results also show that the video quality in our system is much better than that in the other two systems. Our P2P-based approach is also distributed, scalable, cost effective, and aware of the performance.
6522316
Visual echo cancellation in a projector-camera-whiteboard system
We propose to incorporate a whiteboard into a projector-camera system. The whiteboard serves as the writing surface (input) as well as the projecting surface (output). The ability to write and draw on top of computer-projected content opens up many new opportunities for real-time collaborations between people located on-site and remotely. Such applications inevitably require extracting handwritings from video images that contain both handwritings and the projected content. By analogy with echo cancellation in audio conferencing, we call this problem visual echo cancellation. This paper presents one approach to accomplish the task. Our visual echo cancellation algorithm estimates the incident light and derives the surface albedo based on both incident light and reflection. By estimating the albedo, we can extract the writings and recover their colors. Our approach includes two basic components of projector-camera systems: geometric calibration and color calibration. The first one solves the mapping between the position in the camera view and the position in the projector screen, while the second one solves the mapping between the actual color of the projected content and that seen by the camera.
3877390
Distributed meetings: a meeting capture and broadcasting system
The common meeting is an integral part of everyday life for most workgroups. However, due to travel, time, or other constraints, people are often not able to attend all the meetings they need to. Teleconferencing and recording of meetings can address this problem. In this paper we describe a system that provides these features, as well as a user study evaluation of the system. The system uses a variety of capture devices (a novel 360° camera, a whiteboard camera, an overview camera, and a microphone array) to provide a rich experience for people who want to participate in a meeting from a distance. The system is also combined with speaker clustering, spatial indexing, and time compression to provide a rich experience for people who miss a meeting and want to watch it afterward.