Mabo Robert Ito

A chirp scaling approach for processing squint mode SAR data

Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The nonlinear FM filtering method is more accurate but adds a filtering step to the chirp scaling algorithm, although the extra computation is less than that of a time domain residual compression filter. The nonlinear FM pulse method consists of changing the phase modulation of the transmitted pulse, thus avoiding an increase in computation. Simulations show both methods significantly improve resolution width and sidelobe level, compared with existing SAR processors for squint angles above 10 deg for L-band and 20 deg for C-band.

Observation of perturbations in a lumped-element model of the vocal folds with application to some pathological cases.

In this paper a mass-spring model is developed that is a hybrid of the two-mass and the longitudinal string models, proposed by Ishizaka and Flanagan [Bell Sys. Tech. J. 51, 1233-1268 (1972)] and Titze [Phonetica 28, 129-170 (1973)], respectively. The model is used to simulate the vibratory motion of both the normal and asymmetric vocal folds. Mouth-output pressure, lateral tissue displacement, phase plots, and energy diagrams are presented to demonstrate the interaction between vocal fold tissue and the aerodynamic flow between the folds. The results of the study suggest that this interaction is necessary for sustained large amplitude oscillation because the flow supplies the energy lost by the tissue damping. Tissue mass and stiffness were varied locally or uniformly. Decreased stress in the longitudinal string tension produced subharmonic and chaotic vibrations in the displacement, velocity and acceleration phase diagrams. Similar vibratory characteristics also appeared in pathological speech data analyzed using time domain jitter and shimmer measures and a harmonics-to-noise ratio metric. The subharmonics create an effect that has been perceptually described as diplophonia.

Dynamics of load-sensitive adaptive routing

Shortest path first (SPF) routing protocols, such as OSPF and IS-IS are currently the dominant intra-domain IP routing protocols and are widely used in the ISP backbones. Although the traffic on the Internet is highly dynamic, OSPF and IS-IS are not adaptive to the changing traffic, because the shortest path generated by these protocols are based on the link weights, which are fixed and usually can not be changed during network operation. This paper investigates a way of changing the weights in OSPF/IS-IS adaptively according to the changing traffic load on the links. The feedback effect and the stability issue of adaptive routing are analyzed from a control system point of view. The paper shows why minimal-delay adaptive routing, such as the routings in the early ARPANET, is not stable, and proposes some techniques to make our load-sensitive adaptive routing (LSAR) stable. Finally, the performance of LSAR is evaluated by simulation. The result shows that LSAR can significantly improve the QoS of the network by increasing network throughput and reducing packet drop ratio.

QoS control for video and audio communication in conventional and active networks: Approaches and comparison

Various levels of Quality of Service (QoS) can be provided within a network by using integrated services, differentiated services, and active networking approaches. While these three approaches have been presented in several articles, comparison among them is lacking. Therefore, this article examines these three approaches for both their key functionality and their relative strengths and weaknesses of QoS control techniques for video and audio. Future research directions of each approach for supporting QoS for video and audio traffic are also discussed.

Parallel synthetic aperture radar processing on workstation networks

Synthetic aperture radar (SAR) signal processing poses a significant challenge due to its very large computation and data storage requirements. This paper presents the computational requirements of a typical high resolution satellite SAR data processing scenario. A classification of approaches to partitioning the SAR problem for parallel processing is given. The suitability of networks of workstations (NOW) for SAR processing is analyzed for a number of partitioning approaches. The network throughputs required to support SAR processing on NOW are derived. SAR processing is found to demand extremely high network throughput that is difficult to achieve with todays technology.

A multiprocessor approach for meeting the processing requirements for OSI

To meet the increased communication processing requirements of high-speed networks, a multiprocessing network interface is considered for processing multiple layers of a communication protocol stack. In particular, the processing of the open systems interconnection (OSI) layers 2 to 6 on the network interface are considered. OSI processing is computationally expensive because of the inclusion of the transfer syntax conversion at the presentation layer. The approach taken is to process different packets in parallel. The results obtained from simulations indicate that the approach has promise for OSI processing at higher rates. >

Application-aware buffer management: new metrics and techniques

An important issue for video transmission over IP networks is preservation of perceived video quality despite packet loss. Packet loss can be detrimental to compressed video. However, reducing packet loss to a very low level is difficult with current loss control techniques. Furthermore, even a very low objective loss probability can still seriously distort perceived video quality. This paper presents two buffer management schemes using video characteristics. They increase maximum loss tolerance for a desired level of video quality, providing better quality at equal loss ratios, when compared to a conventional buffer management scheme. Meanwhile, service fairness and network efficiency are also improved.

Parallel Region Execution of Loops with Irregular Dependencies

Several compile time transformations of loops with simple dependencies have been developed in order to expose possible parallelism in these loops. However, once an irregular data dependence is detected, no attempt is usually made to extract any parallel thread from the loop. In this paper, we present the parallel region execution, a new compile time approach for improving the execution of loops with complex dependencies. It consists of dividing the iteration space of the loop into parallel regions and serial regions, where all the iterations in the parallel regions can be fully executed in parallel. Our parallel region execution technique has been tested on the MasPar machine for various examples and generally resulted in a large speedup.

Identification of Metallic Spheroids by Classification of Their Electromagnetic Induction Responses

An investigation into the feasibility of applying pattern recognition concepts to the classification of metallic objects by their electromagnetic induction responses was performed. The effect on the response of a limited set of steel spheroids due to various factors such as object shape, size, and orientation was examined and a pattern recognition scheme based on these results was proposed. Implementation of the scheme involved the development of a novel extension to the nearest mean vector type of classifier in which the concept of the class mean as a point in feature space was generalized to be a curve. The resultant pattern recognition scheme was tested on a representative test set which included 815 responses, corresponding to 104 variations in object and orientation. A success rate of greater than 96 percent was achieved. It is noted that the classifier extension developed provides a viable approach to classification of responses that very continuously with respect to a single parameter.

Improved single-trial signal extraction of low SNR events

Initial investigations of Birchs outlier processing method (OPM) have demonstrated an ability to extract a special class of finite-duration signals from colored noise processes. This special class of signals are low SNR signals whose shapes and latencies can vary dramatically from trial to trial. Such signals, termed highly variable events (HVE) in the present paper, are commonly found in physiological signal analysis applications. The present paper identifies that the OPM produces suboptimal HVE estimates due to its use of time-invariant influence functions and demonstrates that the addition of time-varying influence functions (TVIFs) produce improved estimates. Simulation experiments with signals in white and colored noise processes were used to demonstrate the modified OPM algorithms superior performance compared to the performance of the original algorithm and to the performance of a time-invariant minimum mean-square-error (MMSE) filter for linear and stationary processes. The simulation results indicate that the OPM algorithm with TVIFs can extract HVEs from a linear and stationary process for SNR levels above /spl minus/2.5 dB and can work effectively as low as /spl minus/10.0 dB in certain situations. >