Dai Qionghai

Nonexistence of cross-term free time-frequency distribution with concentration of Wigner-Ville distribution

Wigner-Ville distribution (WVD) is recognized as being a powerful tool and a nucleus in time-frequency representation (TFR) which gives an excellent time-frequency concentration, and more importantly, has many desirable properties. A major shortcoming of WVD is the inherent cross-term (CT) interference. Although solutions to this problem from the bulk of contributions to the literature concerning TFR are currently available, none has been able to completely eliminate the CT’s in WVD. It is therefore a common belief that if there exists an auxiliary time-frequency distribution (TFD) which has the same auto-terms (AT’s) as that in WVD, but has CT’s with the opposite sign, then, by adding the auxiliary TFD to WVD, an ideal TFD, which preserves the concentration of WVD while annihilating the CT’s, is readily obtained. However, we prove that the auxiliary TFD does not exist. Moreover, it is found that in general, CT free joint distributions with their concentrations close to that of WVD do not exist either.

BulkTree: An overlay network architecture for live media streaming

Peer-to-peer (P2P) systems are now very popular. Current P2P systems are broadly of two kinds, structured and unstructured. The tree structured P2P systems used technologies such as distributed hash tables (DHT) and hierarchical clustering can search the required target quickly, however, in a tree, the internal node has a higher load and its leave or crash often causes a large population of its offspring’s problems, so that in the highly dynamic Internet environment the tree structure may still suffer frequent breaks. On the other hand, most widely used unstructured P2P networks rely on central directory servers or massive message flooding, clearly not scalable. So, we consider both of the above systems’ advantages and disadvantages and realize that in the P2P systems on node may fail easily, but that when a number of nodes organized as a set, which we call “super node”, the set is robust. Super nodes can be created and updated aware of topology-aware, and used with simple protocol such as flooding or “servers” to exchange information. Furthermore the entire robust super node can be organized into exquisite tree structure. By using this overlay network architecture, P2P systems are robust, efficient, scalable and secure. The simulation results demonstrated that our architecture greatly reduces the alteration time of the structure while decreasing the average delay time, compared to the common tree structure.

An application layer multicast routing algorithm based on genetic algorithms

The application layer multicast routing problem is a multi-objective optimization problem. Most existing protocols are based on simple geographical rules and focus on either tree cost or application load balance performance. Little attention is pay to the lower level performance. The paper analyzes the constraints on multicast routing, then formalizes three functions to evaluate an application layer multicast tree on three indexes, cost, application layer load balance and network layer load balance, then generates one fitness function to describe the trees overall performance. Then the paper proposes the ALMR-GA algorithm, a novel application layer multicast routing approach based on genetic algorithms. Numerical simulations show that, compared with existing routing algorithms, the proposed algorithm reduces the trees cost while satisfying the load balance constraints

DOPPLERLET BASED TIME-FREQUENCY REPRESENTATION VIA MATCHING PURSUITS

A new time-frequency representation called Dopplerlet transform, which uses the dilated, translated and modulated windowed Doppler signals as its basis functions, is proposed, and the Fourier transform, short-time Fourier transform (including Gabor transform), wavelet transform, and chirplet transform are formulated in one framework of Dopplerlet transform accordingly. It is proved that the matching pursuits based on Dopplerlet basis functions are convergent, and that the energy of residual signals yielded in the decomposition process decays exponentially. Simulation results show that the matching pursuits with Dopplerlet basis functions can characterize compactly a nonstationary signal.

Light field compression based on prediction propagating and wavelet packet

A novel data compression scheme of light field is presented. Different from the prior codecs, we perform image predicting and data coding in a set of subbands not directly in original images. In our approach, the original images are decomposed into subbands using wavelet packet transform, and the corresponding wavelet packet bases are divided into two parts: the predictable bases and the unpredictable bases by some criterions. In coding, a propagating algorithm and a rhombuses structure is used, and the subbands corresponding to the basis in predictable and unpredictable bases are added in sequence by relative energy until the reconstructing images meet the pre-established reconstruction quality. Experiments for two standard light fields verify the efficiency of our approach.

Developments and prospects of high-performance detection imaging and identification

High-performance detection imaging and identification is one of the frontier areas in modern information science. It has developed rapidly in recent years, and the urgent need for its applications has accelerated the development. In this paper, four key areas of high-performance imaging detection and identification, namely multi-dimensional microwave detection imaging, weak signal detection and recognition, multi-mode imaging theory and information reconstruction, and computational imaging theory and methods, are systematically expounded in the areas of concept and content, development status both at home and abroad, current popularity and difficulty, typical applications, and future developing trends. In addition, related scientific issues are discussed and summarized. Although the specific problems faced in each field differ from each other, some common and fundamental issues, which should be investigated, include the interaction mechanism between the imaging measures and the target, the acquisition mechanism of detection-imaging data, and target-feature extraction and reconstruction after detection imaging.

An Adaptive Hierarchical Clustering Protocol for Multimedia Overlay Multicast Applications

Adaptive hierarchical clustering algorithm (AHCA) maps a flat topology to a hierarchical tree though output trees are incontrollable and are not suitable for multimedia. Prune-relocate operation and top topologies operation are proposed in this paper to improve AHCA protocol and generate OM-AHCA trees. Numerical simulations show that OM-AHCA trees are compromise between AHCA trees and single-level topology flat protocol trees, which optimize the overall performance of single-level flat protocol and improve the degree metric of AHCA trees

Robust adaptive tracking for nonlinear systems using dynamic neural networks

Abstract A dynamic-neural-network-based control is proposed for a class of affine systems. The approximation for the unknown affine system is studied. The robust learning laws are derived with respect to the modeling errors. The δ - protection and hysteresis technique are used to guarantee the stability of the resulting controller. The features of this approach lie in that neither off-line learning nor sufficiently small initial parameter errors are required. It is proven that the proposed algorithm guarantees all signals bounded in the adaptive loop under any bounded initial conditions. Simulation results are given to verify the effectiveness of the proposed adaptive control algorithm.