Dynamic Spectrum Access in DTV Whitespaces

This is an exciting development because DTV whites- paces are in the low frequency range (50-698 MHz) compared to typical cellular and ISM bands, thus resulting in much better propagation charac- teristics and much higher spectral efficiencies. The FCC has also mandated certain guidelines for short range unlicensed access, so as to avoid any in- terference to DTV receivers. We consider the problem of Wi-Fi like access (popularly referred to as Wi-Fi 2.0) for

enterprizes. We assume that the ac- cess points and client devices are equipped with cognitive radios, i.e., they can adaptively choose the center frequency, bandwidth and power of oper- ation. The access points can be equipped with one or more radios. In this paper, we layout the design of a complete system that (i) does not violate the FCC mandate, (ii) dynamically assigns center frequency and bandwidth to each access point based on their demands and (iii) squeezes the maximum efficiency from the available spectrum. This problem is far more general than prior work that investigated dynamic spectrum allocation in cellular and ISM bands, due to the non-homogeneous nature of the whitespaces, i.e., different whitespace widths in different parts of the spectrum and the large range of frequency bands with different propagation characteristics. This calls for a more holistic approach to system design that also accounts for frequency dependent propagation characteristics and radio frontend char- acteristics. In this paper, we first propose design rules for holistic system design. We then describe an architecture derived from our design rules. Finally we propose demand based dynamic spectrum allocation algorithms with provable worst case guarantees. We provide simulation results show- ing that (i) the performance of our algorithm is within 94% of the optimal in typical settings and (ii) and the DTV whitespaces can provide signifi- cantly higher data rates compared to the 2.4GHz ISM band. Our approach is general enough for designing any system with access to a wide range of spectrum. CategoriesandSubjectDescriptors: C.2.0 [General]: Data Com- munications; C.2.1 [Computer Communication Networks]: Net- work Architecture and Design-Wireless communication General Terms: Design, Algorithms 1. INTRODUCTION Across the world, countries are migrating from analog to digital television broadcasts. For example, in the US, this transition hap- pened on June 12, 2009; while in the UK, this transition is slated to happen in a phased manner from 2008 to 2012. In analog trans- Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. MobiCom’09, September 20–25, 2009, Beijing, China. Copyright 2009 ACM 978-1-60558-702-8/09/09 ...$10.00....

Website: www.bell-labs.com | Filesize: -
No of Page(s): 12
Download Dynamic Spectrum Access in DTV Whitespaces: Design ... - Bell Labs.pdf

Understanding SAP R/3 A Tutorial for Computer Scientists

Learning Objectives Participants will
- break the "language barrier" of R/3 terminology
- understand R/3's fundamental architectural, database and language concepts
- be able to relate R/3 to their own research and development work
- have a conceptual basis and reference material for a further study of R/3

History of SAP Software
1972 SAP “R/1”
• Innovation = Standard Software and Real Time Computing
1983 SAP R/2
• Innovation = Integration of Applications (Mainframe-based)
1989 SAP R/3
• Innovation = Relational Database, Client-/Server-Architecture, Platform Independence

Download pdf Understanding SAP R/3 A Tutorial for Computer Scientists

MAPLE TUTORIAL FOR MATH 243

Differentiation, Integration, Editing Start Maple.
To differentiate sin(x2) type diff( sin(x^2), x); hit Return
The ←, →, ↑, ↓ keys may be used to navigate in the worksheet and the Backspace, Delete keys may be used to correct typing errors. Don’t forget the semicolon - every command ends with a semicolon. To compute definite and indefinite integrals use int( sin(x), x= 0..Pi ); and hit Return int( a*x^2, x ); and hit Return

Note that Pi (upper case P) is the symbol used for π in Maple. The first command computes the definite integral and the second command computes the indefinite integral. Notice, in the second command, ax2 could have been integrated with respect to x or a. One convenient editing trick is the following. Suppose we wish to differentiate xsin(x3). We have already differentiated sin(x
2) - so using the ← ↑ → ↓, keys on the right hand side of the keyboard, move the cursor to that line. Then using the Backspace, Delete, and arrow keys modify that line to read

Download

Using LaTeX to Create Quality PDF Documents

This article is devoted to methods of creating fine quality interactive pdf documents using LATEX. For individuals who write technical material, TEX and LATEX are the idealauthoring tools. Even though this article is written primarily for LATEX users, people who prefer pure TEX may derive much from this article as well. I, myself, prefer AMS-TEX; even so, there is no denying the power, convenience and utility of LATEX.

Beyond the question of the content of your document (content being of premier importance), what elements go into making an attractive document suitable for the www? Page Layout A document not meant to be printed but to be viewed over the Internet must be comfortable enough to the eyes to be read over long periods of time; therefore, making a good choice for page layout is certainly important.
Color Emphasis is a traditionalway of attracting the attention of the reader to a particularly important point. We discuss the ways of...

Download

GPGPU – Basic Math Tutorial

The goal of this tutorial is to explain the background and all necessary steps that are required to implement a simple linear algebra operator on the GPU: saxpy() as known from the BLAS library. For two vectors x and y of length N and a scalar value alpha, we want to compute a scaled vector-vector addition: y = y+alpha∗x. The saxpy() operation requires almost no background in linear algebra, and serves well to illustrate all entry-level GPGPU concepts. The techniques and implementation details introduced in this tutorial can easily be extended to more complex calculations on GPUs.

This tutorial is based on OpenGL, simply because the target platform should not be limited to MS Windows. Most concepts explained here however translate directly to DirectX. This tutorial is not intended to explain every single detail from scratch. It is written for programmers with a basic understanding of OpenGL, its state machine concept and the way OpenGL models the graphics pipeline. For a good overview and pointers to reading material, please refer to the GPGPU community web page 1 .Updates of this tutorial are available on my homepage.

Download

How to Study Mathematics

Before I get into the tips for how to study math let me first say that everyone studies differently and there is no one right way to study for a math class. There are a lot of tips in this document and there is a pretty good chance that you will not agree with all of them or find that you can’t do all of them due to time constraints. There is nothing wrong with that. We all study differently and all that anyone can ask of us is that we do the best that we can. It is my intent with these tips to help you do the best that you can given the time that you’ve got to work with.

Now, I figure that there are two groups of people here reading this document, those that are happy with their grade, but are interested in what I’ve got to say and those that are not happy with their grade and want some ideas on how to improve. Here are a couple of quick comments for each of these groups.

If you have a study routine that you are happy with and you are getting the grade you want from your math class you may find this an interesting read. There is, of course, no reason to change your study habits if you’ve been successful with them in the past. However, you might benefit from a comparison of your study habits to the tips presented here.

If you are not happy with your grade in your math class and you are looking for ways to improve your grade there are a couple of general comments that I need to get out of the way before proceeding with the tips. Most people who are doing poorly in a math class fall into three main categories

Download

Discourse Phenomena in Tutorial Dialogs on Mathematical Proofs

Dialogs about problem solving in mathematics are characterized by a mixture of telegraphic natural language text and embedded formal expressions. Behaving adequately in such an environment is extremely important for tutorial systems, as follows from Moore’s empirical findings which show that flexible natural language dialog is needed to support active learning [9]. However, most state-of-the-art tutorial systems are only able to process limited forms of dialogs, either menu-based or requiring exact wordings [10,2,6].

Motivated by the lack of empirical data, we have collected a corpus of dialogs with a simulated tutoring system for teaching proofs in naive set theory, to identify genre-specific variants of linguistic phenomena which impose specific requirements on natural language dialog management. This work is embedded in a project whose goal is to develop a mathematical tutoring system with flexible natural language dialog. The outline of this paper is as follows. We first present the aims of our project. Next, we describe an experiment in which we collected a corpus of natural language tutorial dialogs. We follow with an analysis of the phenomena observed. Finally, we discuss challenges for natural language dialog management.

Download

Beginner's Mathematica Tutorial

This document is designed to act as a tutorial for an individual who has had no prior experience with Mathematica. For a more advanced tutorial, walk through the Mathematica built in tutorial located at Help > Tutorial on the Mathematica Task Bar.
Starting the Program
1. Start Mathematica. After the program starts, you should see something similar to that shown in Figure 1.
2. It is possible that the Basic Input Palette is not visible at startup. To activate this window, go File > Palettes > Basic Input

Using Mathematica
1. Mathematica is a symbolic manipulator. To assign a variable, simply type it in the Input Window. The enter in the command, you need to hit “Shift + Enter”.
1. Type in “x = 1” then hit “Shift + Enter”
2. Type in “y = a+b;” then hit “Shift + Enter” (note the semicolon here!)
3. Type “z = x + y” then hit “Shift + Enter”

Download

WME: Web-based Mathematics Education

An Idea Whose Time Has Come
• Mathematics teachers and students need help in many countries.
• Availability and standardization of the Web and the Internet have grown and evolved sufficiently.
• Maturing technologies: MathML, ECMAScript, DOM, SVG, XML, CSS, Web Services, ...
• Symbolic and numerical computation systems, have matured and become Internet Accessible.
• Decreasing cost and increasing speed of WAN, LAN, and wireless networking.
• Schools in many places have begun to deploy Internet/Web in classrooms.

Web Helps Math Edu
The Web offers helpful materials for Mathematics teaching/learning.
• The Ohio Resource Center for Mathematics, Science, and Reading provides online resources for mathematics education.
• Mathematics section of the US Department of Education site.
• The National Science Foundation’s Math Is Power.
• The IES sponsored Education Resources Information Center, an extensive literature database.
• The Eisenhower National Clearinghouse for Mathematics and Science Education (ENC) links to lesson plans and activities.

Download

MATHEMATICAL SKILLS Tutorial

To a mathematician math is an end in itself; to the chemist and chemistry student it is a means to an end: a tool. Little in chemistry can be studied and understood without the aid of mathematics. Since math will be an important tool for you it is best if you learn to use this tool efficiently.

Efficiency at doing anything comes through practice; you learn to do something by doing it. The problems in this Tutorial are for your practice. You should do these problems over and over until you can do them automatically. Then when the time comes to use these skills in a chemistry problem you can pay attention to the principle illustrated by the problem and not get lost in the use of math.

If you have to spend what seems like an extraordinary amount of time on these problems, then, definitely, you need to practice and the time spent will repay you many times over during the semester. It may even make the difference between doing well and dropping out. The two math skills covered in this Tutorial are: (1) exponential arithmetic and (2) significant figures.
EXPONENTIAL ARITHMETIC: The basics are given in Appendix A, section A.1, pp 1012-1014, of your lecture text.

Download

MathMl Presenting and Capturing Mathematics for the Web

Document Markup for Mathematics
• Problem: Mathematical Vernacular and mathematical formulae have more structure than can be expressed in a linear sequence of standard characters
• Definition (Document Markup)
Document markup is the process of adding codes to a document to identify the structure of a document or the format in which it is to appear

Document Markup Systems for Mathematics
• M$ Word/Equation Editor: WYSYWIG, proprietary formatter/reader
+ easy to use, well-integrated
– limited mathematics, expensive, vendor lock-in
• TEX/LATEX: powerful, open formatter (TEX), various readers (DVI/PS/PDF)
+ flexible, portable persistent source, high quality math
– inflexible representation after formatting step
• HtML+GIF: server-side formatting, pervasive browsers
+ flexible, powerful authoring systems LATEX/Mathematica/...
– limited accessibility, reusability

Download

A Tutorial on Mathematical Modeling

It is the quintessence of science, engineering, and numerous other disciplines to make quantitative observations, record them, and then try to make some sense out of the resulting dataset. Quite often, the latter is an easy task, due either to practiced familiarity with the domain or to the fact that the goals of the exercise are undemanding. However, when working at the frontiers of knowledge, this is not the case. Here, one encounters unknown territory, with maps that are sometimes poorly defined and always incomplete.

The question posed above is nontrivial; the path from observation to understanding is, in general, long and arduous. There are techniques to facilitate the journey but these are seldom taught to those who need them most. My own observations, over the past twenty years, have disclosed that, if a functional relationship is nonlinear, or a probability distribution something other than Gaussian, Exponential, or Uniform, then analysts (those who are not statisticians) are usually unable to cope. As a result, approximations are made and reports delivered containing conclusions that are inaccurate and/or misleading.

With scientific papers, there are always peers who are ready and willing to second-guess any published analysis. Unfortunately, there are as well many less mature disciplines which lack the checks and balances that science has developed over the centuries and which frequently address areas of public concern. These concerns lead, inevitably, to public decisions and warrant the best that mathematics and statistics have to offer, indeed, the best that analysts can provide. Since Nature is seldom linear or Gaussian, such analyses often fail to live up to expectations.

Download

Fast Fourier Transforms in Mathematica

This tutorial demonstrates how to perform a fast Fourier transform in Mathematica. The example used is the Fourier transform of a Gaussian optical pulse. First, define some parameters. Note that all wavelength values are in nm and all time is in fs. Thus the speed of light c is 300 nm/fs and all frequencies w is thus represented in radians/fs. The fundamental wavelength in interest, lo, is 800 nm with its corresponding frequency wo. For all values the unit for time will be femtosecond, the unit of length nanometers, and the unit for power is Watts.

c = 300;
λo = 800;
ωo = 2 π c
λ o;
ωo êê N 2.35619
Since a Fast Fourier Transform (FFT) is used, one must be careful to sample the electric field properly. To prevent any aliasing, the range is set such that the value of the pulse electric field is approximately zero at the ends of the range. Define the temporal step dt that the pulse electric is sampled in order to prevent aliasing. Also, the FFT requires that the number of points that sample the pulse, num, must be a power of two. In this case num=2048

Download

Radiological Toolbox User's Manual

A toolbox of radiological data has been assembled to provide users access to physical, chemical, anatomical, physiological and mathematical data relevant to the radiation protection of workers and member of the public. The software runs on a PC and provides, through a single graphical interface, quick access to contemporary radiation protection data and the means to extract these data for further use in computations and analysis. The numerical data, for the most part, are stored within databases in SI units. However, the user can display and extract values in non-SI units. This second release of the toolbox includes additional computational capabilities and numerical data of general interest. The toolbox was developed for the U.S. Nuclear Regulatory Commission.

The Radiological Toolbox, hereafter referred to as the Rad Toolbox or simply toolbox, was developed for the U.S. Nuclear Regulatory Commission (NRC). This computer application provides access to physical, chemical, anatomical, physiological and mathematical data (and models) relevant to the protection of workers and the public from exposures to ionizing radiation. A graphical interface enables viewing of the data and the means to extract data for further use in computations and analysis. The numerical data, for the most part, are stored in SI units. However the user can display and extract the data using non-SI units. The data are stored in Microsoft Access databases and in flat ASCII files. This second release of the toolbox features additional computational capabilities and numerical data of interest.

Download