Showing papers by "Andreas Spanias published in 2002"

Smart-antenna systems for mobile communication networks. Part 1. Overview and antenna design

Abstract: This paper focuses on the interaction and integration of several critical components of a mobile communication network using smart-antenna systems. This wireless network is composed of communicating nodes that are mobile, and its topology is continuously changing. One of the central motivations for this work comes from the observed dependence of the overall network throughput on the design of the adaptive antenna system and its underlying signal processing algorithms. Part 1 of this two-part paper gives a brief overview of smart-antenna systems, including the different types of smart-antenna systems, and the reason for their having gained popularity. Moreover, details of typical antenna array designs suitable for the wireless communication devices are included in this part.

Smart antenna system analysis, integration and performance for mobile ad-hoc networks (MANETs)

Abstract: This paper focuses on the interaction and integration of several critical components of a mobile ad-hoc network (MANET) using smart antenna systems. A MANET is a wireless network where the communicating nodes are mobile and the network topology is continuously changing. One of the central motivations for this work comes from the observed dependence of the overall network throughput on the design of the adaptive antenna system and its underlying signal processing algorithms. In fact, a major objective of this work is to study and document the overall efficiency of the network in terms of the antenna pattern and the length of the training sequence used by the beamforming algorithms. This study also considers in sufficient detail problems dealing with the choice of direction of arrival algorithm and the performance of the adaptive beamformer in the presence of antenna coupling effects. Furthermore, the paper presents strategies and algorithms to combat the effects of fading channels on the overall system.

Smart-antenna system for mobile communication networks .Part 2. Beamforming and network throughput

Abstract: Part 1 of this paper provided an overview of smart-antenna systems, and presented a planar array as a design example. In addition, Part 1 discussed the potential of smart antennas with regard to providing increased capacity in wireless communication networks. Part 2 introduces the signal-processing aspects of the antenna array. In particular, it describes the utility of direction-of-arrival algorithms in array-antenna systems, and gives an overview of the signal-processing algorithms that are used to adapt the antenna radiation pattern. The adaptive-algorithm descriptions are accompanied by simulation results obtained for a specific network topology. In particular, the antenna system is simulated assuming a mobile network topology that is continuously changing. Basic results presented are the dependence of the overall network throughput on the design of the adaptive-antenna system, and on the properties of the adaptive-beamforming algorithms and associated antenna patterns.

On-line laboratories for speech and image processing and for communication systems using J-DSP

Abstract: J-DSP is a Java-based object-oriented programming environment that was developed at Arizona State University for use in the undergraduate DSP class [A Sapnias et al, June 2000] In this paper, we describe innovative software extensions on J-DSP to accommodate on-line laboratories for speech processing, image processing, and communications systems Significant modifications in the object-oriented GUI of J-DSP that enable simulation of feedback systems are also presented The speech processing functions enable on-line simulations of speech coding algorithms and include PCM and ADPCM quantization as well as more elaborate algorithms such as the LPC and the CELP Image processing functionalities include development of 2-D signal processing capabilities including 2-D-FFT, 2-D-filter design, and 2-D graphics and picture processing Communications functionality covers several aspects of analog and digital modulation and demodulation On-line laboratory exercises have been developed in the aforementioned areas and posted on a web site (http://jdspasuedu) This site also includes on-line evaluation forms for the exercises Statistical and qualitative evaluations that assess the learning experiences of the students that use J-DSP are presented

Partial band interference excision for GPS using frequency-domain exponents

Abstract: Global Positioning System (GPS) receivers for military applications are highly sensitive to hostile jamming. This paper describes a partial band frequency-domain interference excision technique for GPS receivers. This has been demonstrated to be quite effective in field tests. Although the results of the field tests are classified [6] and not presented here, the algorithm is described in the paper along with a series of simulation results that demonstrate the effectiveness of this technique.

A simulation tool for introducing algebraic celp (ACELP) coding concepts in a DSP course

Abstract: This paper presents an educational tool 1 for introducing Code Excited Linear Prediction (CELP) coding concepts in senior undergraduate and graduate DSP-related courses The tool consists of a user-friendly graphical interface along with a complete MATLAB 2 realization of all aspects of the Algebraic CELP G729 algorithm [2] This simulation software is accompanied by a series of computer experiments and exercises that can be used to provide hands-on training to class participants The exercises designed based on the simulation tool may be used by instructors in a class setting to demonstrate key signal processing concepts associated with the processing of telephone-based speech The MATLAB ACELP tool is being used in Arizona State University undergraduate DSP courses as well as in a graduate course on speech coding and in a continuing education short course Evaluation of the tool and the exercises is being performed by an educational software assessment specialist In the last ten years we have witnessed a series of breakthroughs in speech coding followed by several standardization efforts [1] Most of the standardized algorithms are based on CELP coders Although speech coding researchers and practitioners are well aware of the fundamental ideas used in CELP, students do not get much of an opportunity in courses to study these algorithms A software simulation tool, implementing the ACELP algorithm has been developed for the purpose of introducing speech coding and the associated signal processing concepts to both undergraduate and graduate students We choose an Algebraic Code Excited Linear Prediction (ACELP) algorithm as a basis for this educational tool because of the wide proliferation of algebraic codebooks in cellular standards The algorithm was coded in a modular manner and in its entirety using MATLAB The tool is based on a user-friendly graphical user interface (GUI) that allows the student to study and verify through graphics the various aspects of the algorithm such as: the LP analysis, the open-loop pitch search, the adaptive codebook search (pitch search), the fixed codebook search, and the bit allocation patterns We choose MATLAB as the implementation platform because it allows the user to easily understand the complex parts of the algorithm whose function is not

Adaptive antenna systems for mobile ad-hoc networks

Abstract: This paper focuses on the interaction and integration of several critical components of a mobile ad-hoc network (MANET) using smart antenna systems. A MANET is a wireless network where the communicating nodes are mobile and the network topology is continuously changing. One of the central motivations for this work comes from the observed dependence of the overall network throughput on the design of the adaptive antenna system and its underlying signal processing algorithms. In fact, a major objective of this work is to study and document the overall efficiency of the network in terms of the antenna pattern and the length of the training sequence used by the beamforming algorithms. Furthermore, the paper also considers problems dealing with: the choice of direction of arrival algorithm; the performance of the adaptive beamformer in the presence of antenna coupling effects; combating the effects of fading channels on the overall system.

Adaptive eigen-projection algorithms for 1-D and 2-D antenna arrays

Abstract: In this paper, we develop 1-dimensional (1-D) and 2-dimensional (2-D) adaptive algorithms that use gradient projections in select sub-spaces for use in antenna beamforming. The 1-D algorithm is essentially a significantly enhanced version of an eigen-projection algorithm that was previously developed for system identification. The 2-D algorithm is based on a stacked configuration of the enhanced 1-D algorithm. Both algorithms are applied to antenna beamforming of uniform linear and planar arrays. Simulation results show better convergence as well as improved beam properties.

A simulation tool for introducing MPEG - audio (MP3) concepts in a DSP course

Abstract: This paper presents a simulation tool1 for introducing perceptual audio coding concepts in senior undergraduate and graduate DSP courses. The tool consists of a user-friendly graphical interface along with a complete MA TLAB realization of all aspects of the audio MPEG-1 Layer 3 (MP3) algorithm. The tool is accompanied by a series of computer experiments and exercises that can be used to provide hands-on training to class participants. The tool may also be used by instructors in a class setting to demonstrate key signal processing concepts associated with the processing of high-fidelity audio. The MATLAB MP3 tool has been used in Arizona State University undergraduate DSP courses as well as in a graduate course on speech and audio coding and in a continuing education short course. Evaluation of the tool is being performed by an educational software assessment specialist.

Impact of smart antenna designs on network capacity

Abstract: Smart antenna technology is being considered for mobile platforms such as automobiles, cellular phones (mobile unit), laptops, etc. This paper presents a comprehensive effort on smart antennas that examines and integrates antenna array design, digital signal processing algorithms (for angle of arrival estimation and adaptive beamforming), and the impact of these on the network throughput. The results presented are part of a broader project that considers this antenna system in the context of reconfigurable broadband (high-speed) networks.

Sinusoidal analysis-synthesis of audio using perceptual criteria

Abstract: This paper presents a new method for the selection of sinusoidal components in compact representations of narrowband audio. The method consists of ranking and selecting the most perceptually relevant sinusoids. The idea behind the method is to maximize the matching between the auditory excitation pattern associated with the original signal and the corresponding auditory excitation pattern associated with the modeled signal that is being represented by only a few sinusoidal parameters. The proposed component selection methodology is shown to outperform the maximum signal to mask ratio selection strategy in terms of subjective quality.