Lecture 20: Communications

The Digital World of MultimediaProf. Mari Ostendorf

EE299 Lecture 2027 February 2008

AnnouncementsExam etc.

Returning graded exam, HW4, quiz3 & other stuff not picked up earlier; last page is record of grades so farSolutions posted tomorrowHigh = 96, Average = 78 -- GREAT JOB!!!

Grade changes:HWs & Labs: show Po-Han your graded HWsLab3: email me (I may have missed some late docs)Exam: Come to office hours this Friday, or leave me the exam with a note that explains why you deserve more points on a specific problem

No office hours for me tomorrow 2/28

EE299 Lecture 2027 February 2008

GrammiesWinner:

PhonecallHonorable mentions:

Mysong2Board_sax

If you would like to be credited on the class web page, let me know

EE299 Lecture 2027 February 2008

Feedback from Group DiscussionThanks much for your feedback!Things for me to do (this quarter):

Add sound files online, put more Matlab demos onlineLook into how CSE uses MyUW for providing grades (which profs do this?)Talk about why lectures aren’t like homework

Things for you to do:Send me anonymous email suggesting fundamentals that would be good to spend more time on

EE299 Lecture 2027 February 2008

Plan for TodayHW6/Lab6 DiscussionIntro to Communications

EE299 Lecture 2027 February 2008

HW6/Lab6 ProjectPut together a presentation on a paper of your choice from

IEEE SpectrumSignal Processing MagazineCommunications Magazine

Upload the presentation (ppt or pdf) to CollectItProf. Ostendorf will grade this

Do the presentation in lab Mar 4 or 6Your peers will grade you

Write a 2-3 page summary due Mar 15

EE299 Lecture 2027 February 2008

Presentation Tips: SlidesEach slide should take about 1.5-2min a 10 min talk should have about 5-7 slidesEach point you want to make should be on the slides in words (briefly)Don’t have a lot of slides with only words (you must have multimedia)A little animation is good; a lot is distracting. Same with color.

Note: You must do computer projection. Use either ppt or pdf.

EE299 Lecture 2027 February 2008

Oral Presentation TipsSpeak clearly & with reasonable volumeLook at the audience (not the screen)Know your materialPractice with a friend

Tell them to let you know if you have distracting nervous habitsHave them time each slide, so you know where you are spending too little or too much time

EE299 Lecture 2027 February 2008

Intro to CommunicationsChallengesAnalog vs. digitalTransmission technologiesPacket-based communication

EE299 Lecture 2027 February 2008

Communication ChallengesAll communications systems are imperfectSignal is distorted due to

FadingNoise (thermal, weather, ….)Interference of other signals (or of other bits in this signal)Mulitpath (echo)

Goal is to minimize impact of these problems through

Clever design of signals & transmission methodsError detection & correction

EE299 Lecture 2027 February 2008

Examples of Analog CommunicationsLet m(t) be the information signal (message) you want to sendAM radio (amplitude modulation)

Y(t) = Am(t)cos(2πfRt)Frequency shifting to fR region for transmission, shift back at the receiver

FM radio (frequency modulation)Y(t) = Acos[2πfRt + G(m(t))]Trickier frequency shifting

Just as for sampling: limiting the bandwidth is importantFrequency division multiplexing: combining different signals in different frequency bands

EE299 Lecture 2027 February 2008

Digital CommunicationsSending bits: ultimately the implementation is analog, e.g.

0 vs. 1: Cos(100t) vs. cos(200t)Pulse vs. no pulse

000, 001, 010, … cos(2πkf0t)So what is the advantage of digital?

Small problems can be recovered from perfectlyIntermediate detection and retransmission to avoid big problems

Lecture 20:�CommunicationsAnnouncementsGrammiesFeedback from Group DiscussionPlan for TodayHW6/Lab6 ProjectPresentation Tips: SlidesOral Presentation TipsIntro to CommunicationsCommunication ChallengesExamples of Analog CommunicationsDigital Communications