ECEN5533 Modern Communications TheoryLecture #7 9 September 2014Dr. George Scheets

ECEN5533 Modern Communications TheoryLecture #7 9 September 2014Dr. George Scheets

Read 5.6 – 5.9Read 5.6 – 5.9 Scan Design Problem #1Scan Design Problem #1 Problems 5.14 & 5.15 Problems 5.14 & 5.15 Quiz #1 (Chapter 1) [4.5 Quiz #1 (Chapter 1) [4.5 << Uncorrected Scores Uncorrected Scores << 18.5] 18.5]

Remote DL: No later than 11 SeptemberRemote DL: No later than 11 September Reworked Quiz due 16 September (Live)Reworked Quiz due 16 September (Live)

Exam #1Exam #1 Local: 18 SeptemberLocal: 18 September Remote DL: No later 25 SeptemberRemote DL: No later 25 September

ECEN5533 Modern Communications TheoryLecture #8 11 September 2014Dr. George Scheets

ECEN5533 Modern Communications TheoryLecture #8 11 September 2014Dr. George Scheets

Problems 5.16 – 5.18, 5.21 Problems 5.16 – 5.18, 5.21 Quiz #1 (Chapter 1) Quiz #1 (Chapter 1)

Remote DL: No later than 11 SeptemberRemote DL: No later than 11 September Reworked Quiz due 16 September (Live)Reworked Quiz due 16 September (Live)

Exam #1Exam #1 Local: 18 SeptemberLocal: 18 September Remote DL: No later 25 SeptemberRemote DL: No later 25 September

Design Problem #1Design Problem #1 Due 25 September (Live)Due 25 September (Live) Not Later than 2 October (DL)Not Later than 2 October (DL)

ECEN5533 Modern Commo TheoryLesson #9 16 September 2014Dr. George Scheets

ECEN5533 Modern Commo TheoryLesson #9 16 September 2014Dr. George Scheets

Read 2.1 - 2.4Read 2.1 - 2.4 Problems: 2.1, 2.7, 2.9, 2.11Problems: 2.1, 2.7, 2.9, 2.11 Quiz #1 (Chapter 1) Quiz #1 (Chapter 1)

Reworked Quiz due 16 September (Live)Reworked Quiz due 16 September (Live) 1 week after return (DL)1 week after return (DL)

Exam #1 (covers Chapter 1, 5, and Chapter 2 Sampling Theory)Exam #1 (covers Chapter 1, 5, and Chapter 2 Sampling Theory) Local: Next Time!Local: Next Time! Remote DL: No later 25 SeptemberRemote DL: No later 25 September

Design Problem #1Design Problem #1 Due 25 September (Live)Due 25 September (Live) Not Later than 2 October (DL)Not Later than 2 October (DL)

Any graded HW is accepted lateAny graded HW is accepted late Cost is -1 point per working dayCost is -1 point per working day

Design #1: RoboCop RFPDesign #1: RoboCop RFP Design an RF Public Safety Commo systemDesign an RF Public Safety Commo system

for the city of Metropolis.for the city of Metropolis. Info Sinks can be anywhere in cityInfo Sinks can be anywhere in city Provide system analysis for worst case link.Provide system analysis for worst case link.

(0,0)

(59,47)

Info Source(51,39)

Design #1: RoboCop RFPDesign #1: RoboCop RFP

Configure Transmitter Site (1)Configure Transmitter Site (1) Where to locate? Where to locate?

Height of tower f(worst case distance)Height of tower f(worst case distance) Power OutPower Out Uplink center frequencyUplink center frequency Where be the electronicsWhere be the electronics??

Info Source(51,39)

Design #1: RoboCop RFPDesign #1: RoboCop RFP

Path Loss is cubed not squaredPath Loss is cubed not squared (4πd/λ)3

Antenna GainAntenna Gain Two sectorsTwo sectors

Hi GainHi Gain Low GainLow Gain

Design for WorstDesign for WorstCase G/Ls ratio.Case G/Ls ratio.

GHi

GLo

GHi/Ls1

GLo/Ls2

Design #1: RoboCop RFPDesign #1: RoboCop RFP

Configure Standard Receiver SystemConfigure Standard Receiver System 21,200 units21,200 units Specify LNA PreampSpecify LNA Preamp

Converts RF signal to IF or basebandConverts RF signal to IF or baseband IC AmpsIC Amps

Process RF or baseband, output basebandProcess RF or baseband, output baseband All choices have $$$ impactAll choices have $$$ impact

Many extra credit points available Many extra credit points available

Use a Spread Sheet!!!Use a Spread Sheet!!! Can use again (with mods) on Design 2Can use again (with mods) on Design 2 Tie in costs to design choicesTie in costs to design choices

Can see how changes affect costCan see how changes affect cost Get a system (any system) that worksGet a system (any system) that works

Output power Output power >> 1/4 watt & SNR 1/4 watt & SNR >> 32 dB 32 dB Anything over the minimum is Margin!!!Anything over the minimum is Margin!!!

System delivers 1/2 w & 35 dB SNR?System delivers 1/2 w & 35 dB SNR?Increase Margin by 3 dBIncrease Margin by 3 dB

Adjust parameters to reduce CostsAdjust parameters to reduce Costs Get some of those extra credit points!Get some of those extra credit points!

GradingGrading Real World RFP: Real World RFP:

1 team gets full credit1 team gets full credit Everyone else gets a zeroEveryone else gets a zero

Partial credit Partial credit Awarded on Quizzes & TestsAwarded on Quizzes & Tests NOT AWARDED ON DESIGN PROJECTS!NOT AWARDED ON DESIGN PROJECTS!

Real world designs don't get partial creditReal world designs don't get partial credit Either Work or They Don'tEither Work or They Don't

Double check your work!!! Double check your work!!! Use a spreadsheetUse a spreadsheet

Testable MaterialTestable Material

Communication Theory

Lecture Textbook

Homework

Anything inside the circles is fair game...but overlapped areas are more likely.

To Maximize your score…To Maximize your score… Budget your timeBudget your time Tackle all the problemsTackle all the problems

Partial Credit Partial Credit isis awarded awarded Show intermediate resultsShow intermediate results Obtain correct answerObtain correct answer

Tests are full period, 4 pages, 100 pointsTests are full period, 4 pages, 100 points Open book & notesOpen book & notes HW rework for HW rework for << 1/2 of lost points 1/2 of lost points

Low Noise AmpsLow Noise Amps

System TemperatureSystem Temperature

k*Tk*Tsystemsystem*W*Wnn*G*Gsystemsystem = =

Noise power out of systemNoise power out of system TTsystemsystem is referred to the is referred to the front front of an ideal systemof an ideal system

SNRSNRoutout = P = Pr r / k*T/ k*Tsystemsystem*W*Wnn

A high gain device on the front end helps lower A high gain device on the front end helps lower TTsystemsystem

Power Spectrum GPower Spectrum GXX(f)(f)

Key item for analyzing block diagramsKey item for analyzing block diagrams

Tracking Noise PowerTracking Noise Power

1/2∑ 108∑

Cable Amp

12.42(10-15)

24.01(10-15)

36.43(10-15) 18.22(10-15)

96.29(10-15)

114.5(10-15)

114.5(10-7)

Output SNR = 16.40 dB

Tracking Noise PowerTracking Noise Power

108∑ 1/2∑

Amp Cable

12.42(10-15)

96.29(10-15)

108.7(10-15) 108.7(10-7)

24.01(10-15)

108.7(10-7)

54.35(10-7)

Output SNR = 19.64 dB

MultipathMultipath

Multipath (20 m antenna height)Multipath (20 m antenna height)

Multipath (10 m antenna height)Multipath (10 m antenna height)

Urban Ray TracingUrban Ray Tracing

Image Source: IEEE Communications Magazine

Effect of Ionosphere (f < 35 MHz)Effect of Ionosphere (f < 35 MHz)

Line of Sight & Ground Wave

Ionosphere MultipathIonosphere Multipath

"Cue Ball" Earth"Cue Ball" Earth

Using Earth ContoursUsing Earth Contours

RF Link Equations...RF Link Equations...

are accurate forare accurate for Line of Sight Line of Sight Far Field Far Field No Multipath No Multipath

give a useful average forgive a useful average for Line of Sight Line of Sight Far Field Far Field Multipath Multipath

RF Link Equations...RF Link Equations...

can give ball park results forcan give ball park results for No Line of Sight No Line of Sight Far Field Far Field Multipath Multipathifif path loss is increased path loss is increased

Radio Horizon is 4/3 Optical HorizonRadio Horizon is 4/3 Optical Horizon

Analog to Digital Conversion)Part 1...Analog to Digital Conversion)Part 1...

Sampler

analoginputx(t)

discrete timeoutput

xs(t)

transmitter side

SamplingSampling Ideal SamplerIdeal Sampler

Minimum Sampling FrequencyMinimum Sampling Frequency > 2 * W > 2 * Wabsabs

Real World Realizable SamplerReal World Realizable Sampler Unable to build brick wall filtersUnable to build brick wall filters Must sample about 10% faster than 2*WMust sample about 10% faster than 2*Wabsabs

Output is discrete timeOutput is discrete time But contains info to reconstruct originalBut contains info to reconstruct original

Voltage is still Continuous Voltage is still Continuous Infinite Precision → Infinite # of bits/sampleInfinite Precision → Infinite # of bits/sample

Analog to Digital Conversion)Analog to Digital Conversion)

Sampler

analoginputx(t)

discrete time

signal

xs(t)

transmitter side

SourceCoder

bitstream

Analog to Digital ConversionAnalog to Digital Conversion

AnalogLow Pass

Filter

estimateof analog

input

discrete time signal

estimate

receiver side

SourceDecoder

bitstream

Video UndersamplingVideo Undersampling

Typical TV Video has 30 frames/secondTypical TV Video has 30 frames/second Frame = Still PictureFrame = Still Picture

Car CommercialCar CommercialWheel spokes moving the wrong wayWheel spokes moving the wrong wayWheel spokes stationary, car movingWheel spokes stationary, car moving→ fs not high enough→ fs not high enough

24 bit color 224 = 16.78 M colors24 bit color 224 = 16.78 M colors

256 Colors256 Colors

16 Colors16 Colors

Example) Coding aMicrophone Output

Example) Coding aMicrophone Output

time (sec)

m(t) volts (air pressure)

Energy from about 500 - 3,500 Hz.

A/D ConvertorA/D Convertor

time (sec)

m(t) volts (air pressure)

Step #1)Sample the waveform at rate > 2*Max Frequency.Convert samples to a bit stream.Wired telephone voice is sampled at 8,000 samples/second.

1/8000 second

A/D ConvertorA/D Convertor

time (sec)

m(t) volts (air pressure)

Step #2)Convert the sample voltages to a bit stream.Suppose m(t1) = 3.62 volts...

3.62 v

t1

A/D ConverterA/D Converter Simplest technique is PCMSimplest technique is PCM

Wired Telephone SystemWired Telephone System Audio Compact Disks Audio Compact Disks

Pulse Code ModulationPulse Code ModulationRound off to N possible voltages Round off to N possible voltages Equal length Code word is assigned toEqual length Code word is assigned to

each voltageeach voltageN Typically a Power of 2N Typically a Power of 2LogLog22N bits per code wordN bits per code word

A/D Convertor. 1 bit/sample.A/D Convertor. 1 bit/sample.

time (sec)

Example) N = 2. Assign 0 or 1 to voltage.

0 < Voltage < +5v, Assign Logic 1-5v < Voltage < 0, Assign Logic 0

3.62 v, output a 1

t1

Bit Stream Out = 1111110000111...

A/D Convertor. 1 bit/sample.A/D Convertor. 1 bit/sample.Example) N = 2. Assign 0 or 1 to voltage.

Far side gets... 1111110000111 (13 samples)Need to output 13 voltages.What does a 1 represent? A 0?

Receive a 1? Output +2.5 v (mid-range)Receive a 0? Output -2.5 v (mid-range)

Hold the voltage until next sample

0 < Voltage < +5v, Assign Logic 1-5v < Voltage < 0, Assign Logic 0

A/D Convertor. 1 bit/sample.A/D Convertor. 1 bit/sample.

Input to the transmitter.Output at the receiver.

Considerable Round-Off error exists.

+2.5 v

-2.5 v

time (sec)

Example) N = 4. Assign 00, 01, 10 or 11.

2.5 < Voltage < 5 , Assign 110 < Voltage < 2.5, Assign 10-2.5 < Voltage < 0, Assign 00-5 < Voltage < -2.5, Assign 01

3.62 v, Assign 11

t1

Bit Stream Out =11111011111100 000000101011...

+2.5 v

-2.5 v

A/D Convertor. 2 bits/sampleA/D Convertor. 2 bits/sample

A/D Convertor. 2 bits/sample.A/D Convertor. 2 bits/sample.

Input to the transmitter.Output at the receiver.

Receive 11? Output 3.75vReceive 10? Output 1.25vReceive 00? Output -1.25vReceive 01? Output -3.75vReduced Round-Off error exists.

+3.75 v

+1.25 v

-1.25 v

-3.75 v

Wired Telephone Local LoopWired Telephone Local Loop

WWNN = 3.5 KHz = 3.5 KHz

Low PassFilter

SamplerFs = 8 KHz

TwistedPair Cable

NonuniformQuantize256 levels

PCM Coder

8 bits/sample

64 Kbps

Telephone Local Loop: VoiceTelephone Local Loop: Voice

Decode256 levels

Hold1/8000 sec

64 Kbps

Low PassFilter

Analog Out

Compact DiskCompact Disk

WWNN = 20 KHz = 20 KHz

Low PassFilter

SamplerFs = 44.1 KHz

AudioSource

Quantize65,536 levels

Code16 bits/sample

705.6 Kbps

Compact DiskCompact Disk

Decode65,536 levels

Hold1/44,100 sec

705.6 Kbps

Low PassFilter

Analog Out

Audio (from NPR)Audio (from NPR)

"… before a joint session of Congress for "… before a joint session of Congress for his 2nd State of the Union speech, this is his 2nd State of the Union speech, this is actually the first…"actually the first…"

1/8th Second of Voice1/8th Second of Voice

1/8th Second of Voice1/8th Second of Voice

1/8th Second of Voice1/8th Second of Voice

Sampling & Quantizing ExamplesSampling & Quantizing Examples fs = 16 KHzfs = 16 KHz

4096 quantiles 4096 quantiles 256 quantiles (approximate phone quality)256 quantiles (approximate phone quality) 32 quantiles 32 quantiles 4 quantiles (generally 2 levels used!)4 quantiles (generally 2 levels used!)

4096 quantiles4096 quantiles fs = 16 KHzfs = 16 KHz fs = 8 KHz (some interference)fs = 8 KHz (some interference) fs = 2 KHzfs = 2 KHz fs = 1 KHzfs = 1 KHz