Kam Wing Ng

A novel selective motion vector matching algorithm for error concealment in MPEG-4 video transmission over error-prone channels

The performance of MPEG-4 video transmission over error-prone channels is limited by the channel noise. Error concealment is an effective method of combat to these channel errors. In MPEG-4 video coding, motion vectors (MVs) are highly significant for the matching of the missing video block. Thus how to recover the lost MV is an important issue for error concealment in MPEG-4 video communications. Concerning the high block loss ratio (BLR) during video transmission and the matching of edge blocks in video frames, we propose the selective motion vector matching (SMVM) algorithm for MV recovery. It incorporates the status flags of the neighboring pixels of the missing block and constructs new MV sets for block matching. Experimental results show that it is highly effective and significantly outperforms other existing MV recovery methods for error concealment at different BLRs.

An analytical study on optimizing the lookup performance of distributed hash table systems under churn

The phenomenon of system churn degrades the lookup performance of distributed hash table (DHT) systems greatly. To handle the churn, a number of approaches have been proposed to date. However, there is a lack of theoretical analysis to direct how to make design choices under different churn rates and how to configure their parameters optimally. In this paper, we analytically study three important aspects on optimizing DHT lookup performance under churn, i.e. lookup strategy, lookup parallelism and lookup key replication. Our objective is to build a theoretical basis for designers to make better design choices in the future. We first compare the performance of two representative lookup strategies—recursive routing and iterative routing—and explore the existence of better alternatives. Then we study the effectiveness of lookup parallelism in systems with different churn rates and show how to select the optimal degree of parallelism. Owing to the importance of key replication on lookup performance, we also analyze the reliability of the replicated key under two different replication policies, and show how to perform proper configuration. Besides the analytical study, our results are also validated by simulation, and Kad is taken as a case to show the meaningfulness of our analysis. Copyright

Mode-based error-resilient techniques for the robust communication of MPEG-4 video

Transmission of compressed video over error-prone channels requires techniques that are efficient in compressing the video and are robust against the channel errors. The application of MPEG-4 can conform to the bandwidth limitation, but the highly compressed bits will be more susceptible to noise errors. In this paper, we present a mode-based error detection (MED) technique and a mode-based unequal error protection (M-UEP) technique to provide the robust video transmission of MPEG-4 compressed bits over error-prone channels. The MED technique can detect errors effectively and efficiently, which cannot be detected traditionally. Experimental results show that the error-detection ratio is more than 90%, and sometimes even 100%. Concerning the M-UEP, experimental results prove that it can provide better decoded video quality than the traditional unequal error protection technique does. In conclusion, the two proposed techniques are highly effective and efficient for the robust transport of MPEG-4 video over error-prone channels.

Implementation of GAMMA on a massively parallel computer

The GAMMA paradigm is recently proposed by Banâtre and Métayer to describe the systematic construction of parallel programs without introducing artificial sequentially. This paper presents two synchronous execution models for GAMMA and discusses how to implement them on MasPar MP-1, a massively data parallel computer. The results show that GAMMA paradigm can be implemented very naturally on data parallel machines, and very high level language, such as GAMMA in which parallelism is left implicit, is suitable for specifying massively parallel applications.

An efficient error detection technique for MPEG-4 video streams

Video transmission over error-prone channels requires techniques that are efficient in compressing the video and robust against the channel errors. The application of MPEG-4 in video communication can conform to bandwidth limitations, but, on the other hand, the highly compressed bits are more susceptible to noise errors. Therefore, many researchers have been working on error concealment techniques to recover errors caused by noise. However, the errors are always assumed to have been correctly located, which is the precondition for error concealment. We propose a novel error detection technique. This scheme can effectively and efficiently detect some errors which cannot be detected traditionally. Experimental results show that the error detection ratio (EDR) for this type of error is more than 90%, even 100% sometimes.

Analysis and detection of MPEG-4 visual transmission errors over error-prone channels

Transmission of compressed video over error-prone channels requires techniques that are efficient in compressing the video and robust against the channel errors. The application of MPEG-4 in video communication can conform to the bandwidth limitation, but on the other hand the highly compressed bits is more susceptible to noise errors. Therefore many researchers have been working on error resilient and concealment techniques to recover errors caused by noises. However, the errors are always assumed to have been correctly located, which is the precondition for error concealment. In this paper, we propose a novel error detection technique. This scheme can detect some errors effectively and efficiently, which cannot be detected traditionally. Experimental results show that the error detection ratio (EDR) for this type of errors is more than 90%, even 100% sometimes.

A Fault-Tolerance Mechanism for Mobile Agent Systems

The mobile agent paradigm has attracted many attentions recently but it is still not widely used. One of the barriers is the difficulty in protecting an agent from failure because an agent is able to migrate over the network autonomously. In this paper, a novel approach to protect an agent from failure is presented. The main characteristics include low network bandwidth consumption, high flexibility and feasibility to be applied in an open environment

Integrating digital libraries by CORBA, XML and Servlet

In this paper, we describe how we use a mediator-based architecturefor integrating digital libraries. We discuss how we tackle the obstacles of firewalls in the expansion of our system by using XML and Java Servlet, which are used to achieve CORBA general communications and callback features across the firewalls.

A multiparadigm language for developing agent-oriented applications

I/sup +/ is a multiparadigm language for object oriented declarative programming as well as parallel programming. If is an integration of three major programming paradigms: object oriented, logic and functional with salient features for modelling distributed applications, however, I/sup +/ has a number of limitations in developing multi agent applications as well as programming mobile agents. We introduce a dedicated set of primitives necessary for communication among agents and an HTTP based infrastructure to serve mobile agents to I/sup +/. The resultant language is called I* and we argue that I* is a language suitable for the development of agent oriented applications.

A novel motion vector recovery algorithm for error concealment in video transmission

Error concealment is an effective method to combat channel errors for video transmission. In video coding, motion vectors (MVs) are highly significant for the matching of the missing video block. Thus, how to recover the lost MV is an important issue for error concealment in video communications. Concerning the high block loss ratio (BLR) during video transmission and the matching of edge blocks in video frames, we proposed a selective motion vector matching (SMVM) algorithm for MV recovery. It incorporates the status flags of the neighboring pixels of the missing block and constructs new MV sets for block matching. Experimental results show that it significantly outperforms other existing MV recovery methods for error concealment at different BLRs.