Arno Formella

Efficient ray-tracing acceleration techniques for radio propagation modeling

Ray-tracing and uniform theory of diffraction techniques are already widely applied to site-specific radio propagation modeling for wireless applications. Software tools using such techniques may take considerable computation time in the analysis of the propagation conditions in a given environment even for a short mobile terminal route. Efficient acceleration techniques are required to make such analysis tools practical for the design of modern radio systems. To reduce computation time, ray-tracing routines must be applied only to those areas where rays are likely to exist. This is achieved by using ray-path search algorithms prior to performing any actual ray tracing. An efficient ray-path search algorithm is presented. First, a two-dimensional version is described, which is valid for indoor and microcell studies. Then, an extension to the three-dimensional case is explained in detail. Finally, the software tool Radio Tracer using such techniques is briefly described, and some comparisons between experimental results and computed predictions for indoor and outdoor scenarios are shown.

Fast ray tracing for microcellular and indoor environments

We present a very efficient algorithm which calculates deterministically the path losses, delay profiles and other characteristics of a mobile channel. The algorithm can be used both for indoor and outdoor environments. We apply the technique of tracing rays and compute reflections, transmissions and diffractions with the help of geometrical optics, heuristical approximations and the uniform theory of diffraction (UTD).

Automatic detection and classification of grains of pollen based on shape and texture

Palynological data are used in a wide range of applications. Some studies describe the benefits of the development of a computer system to pollinic analysis. The system should involve the detection of the pollen grains on a slice, and their classification. This paper presents a system that realizes both tasks. The latter is based on the combination of shape and texture analysis. In relation to shape parameters, different ways to understand the contours are presented. The resulting system is evaluated for the discrimination of species of the Urticaceae family which are quite similar. The performance achieved is 89% of correct pollen grain classification

Superimposé: a 3D structural superposition server

The Superimposé webserver performs structural similarity searches with a preference towards 3D structure-based methods. Similarities can be detected between small molecules (e.g. drugs), parts of large structures (e.g. binding sites of proteins) and entire proteins. For this purpose, a number of algorithms were implemented and various databases are provided. Superimposé assists the user regarding the selection of a suitable combination of algorithm and database. After the computation on our server infrastructure, a visual assessment of the results is provided. The structure-based in silico screening for similar drug-like compounds enables the detection of scaffold-hoppers with putatively similar effects. The possibility to find similar binding sites can be of special interest in the functional analysis of proteins. The search for structurally similar proteins allows the detection of similar folds with different backbone topology. The Superimposé server is available at: http://bioinformatics.charite.de/superimpose.

Building the 4 processor SB-PRAM prototype

The SB-PRAM is a massively-parallel, uniform memory access (UMA) shared-memory computer. The main ideas of the design are multithreading on the instruction level, hashing of the address space, and combining in the butterfly network. We have built a first research prototype with four physical processors, and thus 128 virtual processors, to demonstrate the feasibility of the concept. The programming environment consists of a FORK compiler for specifying PRAM programs, an extended C compiler and the P4 library. The machine runs a parallel operating system which provides program execution and I/O system calls. The SB-PRAM allows for efficient programs with predictable performance. Some examples are presented. The four-processor prototype is the first step towards a 128-processor machine for which we are adapting the existing hardware.

Generalized Fisheye Views of Graphs

Fisheye views of graphs are pictures of layouted graphs as seen through a fisheye lens. They allow to display, in one picture, a small part of the graph enlarged while the graph is shown completely. Thus they combine the features of a zoom—presenting details— and of an overview picture—showing global structure. In previous work the part of the graph to be enlarged—the focus region—was defined by a focus point. We generalize fisheye views such that the focus region can be defined by a simple polygon and show efficient algorithms to compute generalized fisheye views. We present experimental results on two applications where generalized fisheye views are advantageous: travel planning and ray tracing.

Optimization methods for optimal transmitter locations in a mobile wireless system

A combination of a simple indoor propagation model with different optimization methods enables optimal single and multiple transmitter locations and antenna sectorization in wireless systems.

HPP: A High Performance PRAM

We present a fast shared memory multiprocessor with uniform memory access time. A first prototype (SB-PRAM) is running with 4 processors, a 128 processor version is under construction. A second implementation (HPP) using latest VLSI technology and high speed links shall run at a speed of 96 MHz. To achieve this speed, we first investigate a re-design of the hardware of the SB-PRAM. We then balance processor speed and memory bandwidth by investigating the relation between local computation and global memory access in several benchmark applications. On numerical codes such as Linpack 2 resp. 8 GFlop/s shall be possible with 128 resp. 512 processors, thus approaching processor performance of an Intel Paragon XPS. On non-numerical codes, i.e., circuit simulation and ray tracing, we achieve speedups over a one processor SGI challenge of 35 and 81 for 128 processors and 140 and 327 for 512 processors.

A genetic algorithm approach for feature selection in potatoes classification by computer vision

Potato quality control has improved in the last years thanks to automation techniques like machine vision, mainly making the classification task between different quality degrees faster, safer and less subjective. We present a system that classifies potatoes depending on their external defects and diseases. Firstly, some image processing techniques are used to segment and analyze the potatoes. Then, a classifier is used to decide the group the potato belongs to. For the feature selection task, we have designed an ad-hoc genetic algorithm which maximizes the classification percentage. This approach is used to perform an optimization in the search of the better feature combination. The system shows to be effective in real operation simulations (working with unwashed potatoes covered with dust and sand,), what seems to be a good starting point in the development of the system.

Indoor and outdoor channel simulator based on ray tracing

An efficient algorithm that dynamically calculates all possible ray paths in outdoor (macro- and micro-cells and land mobile satellite, LMS) and indoor environments is presented in this paper. The algorithm is based on the sweep line technique. Additionally a quadtree (bounding box (Athanasiadou, 1995)) division of the study environment is used to reduce search time. For indoor and microcellular environments wall reflections and transmissions as well as diffractions on vertical edges are considered up to the order specified by the user. 2D ray-path search algorithms have been extended to 3D in order to model macrocellular and land mobile satellite environments. For such cases, apart from multiple reflections, transmissions and vertical diffractions, the propagation simulator also takes into account single diffractions on horizontal edges and corners directly visible both from the transmitter and the receiver. Combinations of propagation mechanisms have also been considered in the simulator.