Earticle

The video coding with a bit rates below 10k bps has not been considered as a practical application in commercial communication systems. The main reason is that a user in the present multiple access system is assigned a fixed conceptual channel with the bit rate of speech signal, which is much more than 10k bps such as 16k. Video communication below 10k bps using inexpensive resource is indeed of low caliber of visual quality but is still readable in a small display. This visual quality can be tolerable under the consideration of the convenient receiver and the limit bandwidth for communication. Therefore, the proposed coding strategy in this paper to code the 64*64 binary images is suitable for ubiquitous services.

The aim of this paper is to propose an imperceptible wavelet-based watermarking scheme. In our scheme, we use variation to define the degree of transparence of coefficients of LL band and further determine transparent coefficients of HL3 and LH3 bands. Then, the watermark is embedded into those coefficients. In addition, the modular operation is utilized during watermark embedding. In the experimental results, we simulate some common attacks on the watermarked image. It is shown that our scheme is robust against most attacks; moreover, the watermarked image is highly imperceptible.

Based on assumption of perfect synchronization, a scheme defined as 4-ary Elliptical Phase Shift Keying (4-EPSK) has shown advantage over QPSK on noise performance. However, the analysis also shows that performance of 4-EPSK is vulnerable to synchronization errors. To realize efficient signal detection and simplicity of receiver, in this paper, we propose a timing recovery algorithm for 4-EPSK transmission by employing envelope characteristics of 4-EPSK signal. The proposed technique realizes estimation and recovery of time offset through self-processing envelope of the received signal. The evaluation results demonstrate that the proposed technique is effective when time offset of a received 4-EPSK signal is smaller than half symbol duration.

Live streaming media distribution in a large scale P2P network and the impact on the real-time caused by the dynamicity of peers are still not well resolved. In order to address this problem, a scalable live streaming media distribution service in P2P network is presented. Our approach is that the P2P network combining tree with clusters is designed, and some super-peers are reserved in all clusters. In addition, we adopt the maximum accepted connection number of each super-peer and its average disposing delay to select the optimal father peer, and the limitation of packet discard between super-peers is given. The experiment results show that the distribution service assures the improvement of real-time and scalability in the large-scale P2P network.

Due to the vast size, real-time requirement, QoS consideration, etc., of mobile devices, techniques like multimedia transcoding are developed to satisfy the need of surfing the multimedia services using mobile devices. In this paper, we propose a P2P resource sharing architecture for adapting MPEG-21 digital items in mobile networks. In the proposed P2P architecture, digital items can be shared among heterogeneous networking environments. Meanwhile, digital items can be dynamically adapted according to the networking situation and user’s device capacity. The proposed P2P system introduced a new cache and replacement algorithm for managing adapted digital items, which can smooth the transcoding delay variations of digital items during subsequent resource sharing among different networked devices.

In this paper, we propose a new pairwise key agreement, TLPKA (Tangent Line Pairwise Key Agreement), for establishing a secure link between members in an ad hoc network. With pairwise keys, data transmitted in ad hoc networks can be protected from the eavesdropping of outsiders. These pairwise keys can also be used to authenticate members in ad hoc networks. In addition, due to the property of uniqueness of pairwise keys, it also provides non-repudiation for data transmitting. In our scheme, we propose a new idea for the design of pairwise key agreements in an ad hoc network. Our scheme is based on the geometrical property of the tangent line and the mechanisms in our scheme are inspired by the Shamir secret sharing scheme. Our schemes also provide reciprocal authentication among node communicants. The robustness of our scheme is based on the DH problem and the indefinite solutions in coordinate geometry. In addition, we compare our scheme with other schemes. Although there is a higher overhead associated with our scheme, it maintains a higher security level than the other schemes.

More and more media material is consumed in ubiquitous environment where the service can be experienced over different devices, network conditions, network bearers, etc. Unlike in traditional wireless environments where at least changes of the QoS parameters are controlled by the network, ubiquitous networks are characterized by abrupt changes. Transition from complete disconnectivity to low-cost, high-bandwidth connection can happen in a relatively short time span. Media consumption over such networks are influenced by two, contradictory user requirements. The first requirement is that the users would not like to see quality changes in the media stream. The second requirement is that the user would like to consume the media with the best available quality. This paper presents an adaptation algorithm that aims to reconcile these requirements. Architecture variants of the media adaptation problem and prototyping experiences are also presented.

Communicating with someone via the right communication media seems to be difficult nowadays as people use various mode of communication media and senders do not have any knowledge about receivers’ current communication media, especially in ubiquitous environment. Thus, we propose the method how the most appropriate media to reach the receiver can be selected based on the effective measures. In the paper, a preliminary evaluation of the proposed method is also described to show its effectiveness. We are developing a research prototype system to support the sender with the information of the best reachable media to the receiver.

Nowadays compressed files are very widespread and can be considered, without any doubt, with regard to the Digital Forensic realm, an important and precious source of probatory data. This is especially true when in a digital investigation the examiner has to deal with corrupted compressed files, which have been gathered in the collection phase of the investigative process. Therefore, in the computer forensic field, data recovery technologies are very important for acquiring useful pieces of data which can become, in a court of low, digital evidence. This kind of technology is used not only by law enforcement, but also by the multitude of users in their daily activities, which justify the relevant presence of tools in the software market which are devoted to rescue data from damaged compressed files. However, state-of-the-art data recovery tools have many limitations with regard to the capability of recovering the original data, especially in the case of damaged compressed files. So far, such recovery tools have been based on a schema which controls the signature/header of the file and, thus, provides the offset to the raw compressed data block. As a result, they cannot recover the compressed files if the first part of the raw compressed data block, which pertains to the header, is damaged or the signature/header block is corrupted. Therefore, in order to deal with this issue, we have developed a new tool capable of rescuing damaged compressed files, according to the DEFLATE compression scheme, even though the header block is missing or corrupted. This represents a new interesting opportunity for the digital forensic discipline.