Lee & Varaiya Introducing Signals and Systems The Berkeley Approach Edward A. Lee Pravin Varaiya...

Lee & Varaiya

Introducing Signals and SystemsThe Berkeley Approach

Edward A. LeePravin VaraiyaUC Berkeley

A computer without networking, audio, video, or real-time services.

Lee & Varaiya

Starting PointEE CE CS

ElectronicsOpticsE&MPlasmas

ArchitectureCADSystems

LanguagesAITheory of Computation......

But the juncture of EE and CS is not just hardware.It is also mathematical modeling and system design.

Lee & Varaiya

Intellectual Grouping of EE, CE, CSMultimediaRobotics, Vision

Linear systems

Signal processing

CSControl

ArchitectureCAD for VLSIConfigurable systems

Discrete-event systems

Real-time systemsConcurrent softwareNetworks

LanguagesComplexityAutomataSoftware engineeringCompilers

AlgorithmsOperating systems

GraphicsUser interfacesDatabases

Nonlinear systems

Simulation

Artificial Intelligence

CommunicationsInformation theoryQueueing theory

CircuitsElectronicsDevicesProcess technologyE & MPower systemsPlasmasQuantum & Optical

Lee & Varaiya

Six Intellectual Groupings

•Blue: Computer Science

•Green: Computer Information Systems

•Yellow: Electronic Information Systems

•Orange: Electronic Systems

•Red: Electronics

•Purple: Computer hardware

Lee & Varaiya

(EE 40)

(EECS 20)

(CS 61A) Structure & Interpretation ofSignals & Systems

The Structure and Interpretationof Computer Programs

Introduction toElectronic Circuits

New Introductory Course Needed

Lee & Varaiya

The Roots of Signals and Systems

• Circuit theory• Continuous-time• Calculus-based

Major models• Frequency domain• Linear time-invariant systems• Feedback

Lee & Varaiya

Changes in Content

• Signal•used to be: voltage over time•now may be: discrete messages

• State•used to be: the variables of a differential equation•now may be: a process continuation in a transition

system

• System•used to be: linear time invariant transfer function•now may be: Turing-complete computation engine

Lee & Varaiya

Changes in Intellectual Scaffolding

• Fundamental limits•used to be: thermal noise, the speed of light•now may be: chaos, computability, complexity

• Mathematics•used to be: calculus, differential equations•now may be: mathematical logic, topology,

set theory, partial orders

• Building blocks•used to be: capacitors, resistors,

transistors, gates, op amps•now may be: microcontrollers, DSP cores,

algorithms, software components

Lee & Varaiya

Action at Berkeley

Berkeley has instituted a new sophomore course that addresses mathematical modeling of signals and systems from a very broad, high-level perspective.

The web page at the right contains an

applet that illustrates complex exponentials

used in the Fourier series.

Lee & Varaiya

Themes of the Course

• The connection between imperative (Matlab) and declarative (Mathematical) descriptions of signals and systems.

• The use of sets and functions as a universal language for declarative descriptions of signals and systems.

• State machines and frequency domain analysis as complementary tools for designing and analyzing signals and systems.

• Early and often discussion of applications.

Lee & Varaiya

Role in the EECS Curriculum

eecs 20structure and

interpretation of signals and

systems

eecs 40circuits

cs 61astructure and

interpretation of computer programs

math 55 or CS 70discrete math

math 53multivariable

calculus

math 54linear algebra

& diff. eqs.

math 1acalculus

math 1bcalculus

physics 7amechanics &

physics 7bheat, elec, magn. cs 61b

data structures

cs 61bmachine structures

Required courses for all EECS majors.

helpful

Note that Berkeley has no “computer

engineering” program.

Lee & Varaiya

Current Role in EE

systems

eecs 121digital

communication

eecs 123digital signal processing

eecs 120signals and

systems

eecs 126probability and

random processes

eecs 122communication

networks

eecs 125robotics

Lee & Varaiya

Future Role in EECS (speculative)

systems

eecs 121digital

communication

eecs 123digital media &

signal processing

eecs 120signals and

systems

eecs 126probability and

random processes

eecs 122communication

networks

eecs 125robotics

eecs xxxdiscrete-event

systems

eecs xxxreal-time systems

Lee & Varaiya

Outline

1. Signals2. Systems3. State4. Determinism5. Composition6. Linearity7. Freq Domain8. Freq Response9. LTI Systems10. Filtering 11. Convolution 12. Transforms13. Sampling14. Design15. Examples

Lee & Varaiya

Outline

Lee & Varaiya

Notation

• Sets and functions– Sound : Reals Reals– DigitalSound : Ints Reals– Sampler : [Reals Reals] [Ints Reals]

• Our notation unifies– discrete and continuous time– event sequences– images and video, digital and analog– spatiotemporal models

Lee & Varaiya

Problems with Standard Notation

• The form of the argument defines the domain– x(n) is discrete-time, x(t) is continuous-time.– x(n) = x(nT)? Yes, but…

– X(jw) = X(s) when jw = s– X(ejw) = X(z) when z = ejw

– X(ejw) = X(jw) when ejw = jw? No.

• x(n) is a function– y(n) = x(n) * h(n)– y(n-N) = x(n-N)*h(n-N)? No.

Lee & Varaiya

Using the New Notation

• Discrete-time Convolution :

• Shorthand:

• Definition:

( * )( ) ( ) ( )x y n x k y n kk

x y x y* ( , )Convolution

Convolution Ints Reals Ints Reals

Ints Reals

:[ ] [ ]

Lee & Varaiya

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Analysis of Spring 2000 Offering

• Class standing had little effect on performance.• On average, the GPA of students was neither

lowered nor raised by this class.• Students who attend lecture do better than

those that don’t.• Taking at least one of Math 53, 54, or 55 helps

by about ½ grade level.• Taking Math 54 (linear algebra & differential

eqs.) helps by about 1 grade level (e.g. B to B+).

• Computing classes have little effect on performance.

Lee & Varaiya

Distribution by Class Standing

Class Distribution

freshmen sophmores juniors seniors

Lee & Varaiya

Effect of Class Standingscore vs. standingy = 1.2836x + 74.719

R2 = 0.0093

0 1 2 3 4 5

standing

80 and above: A’s63 and above: B’s62 and below: C’s

176 of the 227 students responded (the better ones).

Lee & Varaiya

Effect of Showing UpStudents who answered the survey were those that showed up for the second to last lab.

• The mean for those who responded was 78, vs. 65 for those who did not respond (two grades, e.g. B to A-).

• The standard deviation is much higher for those who did not respond.

• A t-test on the means shows the data are statistically very significant.

We conclude that the respondents to the survey do not represent a random sample from the class, but rather represent the diligent subset.

Lee & Varaiya

Attendance in Class vs. Score

y = 6.7939x + 46.665

R2 = 0.4006

0 1 2 3 4 5

Attendance

Attendance is measured by presence for pop quizzes, of which there were five.

Lee & Varaiya

Effect on GPA

B range before Sp 2000

B range in EECS 20

On average, students’ GPA was not affected by this class.

Lee & Varaiya

Student Opinion on Prerequisites

Number of students suggesting prerequisite

math 1b math 53 math 54 math 55

series linear algebra

Lee & Varaiya

Differences from Tradition

• No circuits• More discrete-time, some continuous-

time• Broader than LTI systems• Unifying sets-and-functions framework• Emphasis on applications• Many applets and demos• Tightly integrated software lab

Text draft (Lee & Varaiya) and website available.

Lee & Varaiya

Bottom-Up or Top-Down?

Top-down:- applications first- derive the foundations

Bottom-up:- foundations first- derive the applications

Lee & Varaiya

Textbook

Draft available onthe web.

Lee & Varaiya Introducing Signals and Systems The Berkeley Approach Edward A. Lee Pravin Varaiya...

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