ECEN5553 Telecom SystemsDr. George ScheetsWeek #2

Read [3] "A Roadmap to 100G Ethernet at the Enterprise Data Center"

Exam #1 Lecture 15, 21 September (Live)No later than 28 September (Remote DL)

Outline 7 October 2015, Lecture 22 (Live)No later than 14 October (Remote DL)

ECEN5553 Telecom SystemsDr. George ScheetsWeek #2

Read [3] "A Roadmap to 100G Ethernet at the Enterprise Data Center"

Exam #1 Lecture 15, 21 September (Live)No later than 28 September (Remote DL)

Outline 7 October 2015, Lecture 22 (Live)No later than 14 October (Remote DL)

OutlinesReceived

due 7 October (local)14 October (remote)

OutlinesReceived

due 7 October (local)14 October (remote)

0 %

Fiber Optic CableFiber Optic Cable

1 1/4 inch

SC

Physical Layer Ailments...Physical Layer Ailments...

AttenuationAttenuationSignal power weakens with distanceSignal power weakens with distance

DistortionDistortionPulse shapes change with distancePulse shapes change with distance Copper cablingCopper cabling

High frequencies attenuate fasterHigh frequencies attenuate fasterPulses smearPulses smear

Fiber cablingFiber cablingFrequencies propagate at different speedsFrequencies propagate at different speedsDispersion (Pulses change shape)Dispersion (Pulses change shape)

Generating a Square Wave...Generating a Square Wave...

0

1.5

-1.50 1.0

5 Hz+

15 Hz+

25 Hz+

35 Hz

cos2*pi*5t - (1/3)cos2*pi*15t + (1/5)cos2*pi*25t - (1/7)cos2*pi*35t)

Effects of Dispersion...Effects of Dispersion...

0

1.5

-1.50 1.0

5 Hz+

15 Hz+

25 Hz+

35 Hz

cos2*pi*5t + (1/3)cos2*pi*15t + (1/5)cos2*pi*25t + (1/7)cos2*pi*35t)

In this example the 15 and 35 Hz signals have suffered a phase shift (which can be caused as a result of different propagation speeds) with respect to the 5 and 25 Hz signals. The pulse shape changes significantly.

Smearing (a.k.a. Inter-symbol Interference)Smearing (a.k.a. Inter-symbol Interference)

0 20 40 60 80 100 120 140

0

4.5

4.5

zk

z2k

1270 k

outputinput

Pulse energy is no longer confined to a T second time interval.Makes receiver symbol detector's life more difficult.

Examples of Amplified NoiseExamples of Amplified Noise Radio Static (Thermal Noise)Radio Static (Thermal Noise) Analog TV "snow"Analog TV "snow"2 seconds

of White Noise

SNR = Average Signal Power = Infinity Average Noise PowerSNR = Average Signal Power = Infinity Average Noise Power

0 20 40 60 80 100

0

4.5

4.5

z2k

xk

990 k

Binary SignalSequence = 0011010111

SNR = 100SNR = 100

0 20 40 60 80 100

0

4.5

4.5

z2k

xk

990 k

Signal a sequence +1 and -1 volt pulsesFor your info, SSD BER ≈ 0.0

SNR = 10SNR = 10

0 20 40 60 80 100

0

4.5

4.5

z2k

xk

990 k

Signal a sequence +1 and -1 volt pulsesFor your info, SSD P(BE) = 0.000783 = 1/1277

SNR = 1SNR = 1

0 20 40 60 80 100

0

4.5

4.5

z2k

xk

990 k

Signal a sequence +1 and -1 volt pulsesFor your info, SSD P(BE) = 0.1587 = 1/6.3

SNR = .1SNR = .1

0 20 40 60 80 100

0

8.5

8.5

z2k

xk

990 k

Signal a sequence +1 and -1 volt pulsesFor your info, SSD P(BE) = 0.3759

Single Sample Detector: SNR = 1Single Sample Detector: SNR = 1

0 20 40 60 80 100

0

4.5

4.5

990 k

Threshold is placed midway between nominal Logic 1 and 0 values.

Detected sequence = 0011010111 at the receiver,but there were some near misses.

Fall 2002 FinalFall 2002 Final 'Average' based on 1 test chosen at random'Average' based on 1 test chosen at random

126.00 out of 150126.00 out of 150 Analogous with "Single Sample" DetectorAnalogous with "Single Sample" Detector

'Average' based on 10 tests chosen randomly'Average' based on 10 tests chosen randomly109.44 out of 150109.44 out of 150 Analogous with "Multiple Sample" DetectorAnalogous with "Multiple Sample" Detector Average based on 10 samples tends to be more accurate than Average based on 10 samples tends to be more accurate than

"Average" based on 1 sample"Average" based on 1 sample Actual Midterm AverageActual Midterm Average

106.85 out of 150106.85 out of 150

Matched Filter Detector: SNR = 1Matched Filter Detector: SNR = 1

0 20 40 60 80 100

0

4.5

4.5

990 k

Orange Bars are average voltage over that symbol interval.

Averages are less likely to be way off the mark.SSD P(BE) = 0.3759, MFD P(BE) = 0.000783 (10 samples/bit)

Receiver DetectionReceiver Detection SNR tends to worsen with distanceSNR tends to worsen with distance Digital Receiver Symbol DetectorsDigital Receiver Symbol Detectors

Examine received symbol intervals (T sec.)Examine received symbol intervals (T sec.) Decide which of M symbols was transmittedDecide which of M symbols was transmitted Single Sample DetectorsSingle Sample Detectors

Sample each symbol once Sample each symbol once Compare sampled value to a thresholdCompare sampled value to a threshold

Matched Filter DetectorsMatched Filter Detectors (Optimal) (Optimal)Sample each symbol multiple times Sample each symbol multiple times & generate an average & generate an average Compare the average value to a thresholdCompare the average value to a threshold

Channel CapacityChannel Capacity Bandwidth affects usable symbol rateBandwidth affects usable symbol rate

Rapidly changing symbols need hi frequenciesRapidly changing symbols need hi frequencies Baud rate too high? Distortion!!Baud rate too high? Distortion!!

M-Ary allows increased bit rateM-Ary allows increased bit rate Each symbol can represent multiple bitsEach symbol can represent multiple bits

SNRSNR Affects RCVR ability to tell symbols apartAffects RCVR ability to tell symbols apart

Bandwidth & SNR affect usable bit rateBandwidth & SNR affect usable bit rate

Channel Capacity (C)Channel Capacity (C) Bandwidth, Bit Rate, SNR, and BER relatedBandwidth, Bit Rate, SNR, and BER related Channel Capacity defines relationshipChannel Capacity defines relationship

C = Maximum reliable bit rate C = Maximum reliable bit rate C = W*Log C = W*Log22(1 + SNR) bps(1 + SNR) bps

Bandwidth sets the maximum Baud rateIf move too many Baud, symbols will smear.

SNR sets the maximum number ofdifferent symbols (the "M" in M-ary)you can reliably tell apart.

Channel Capacity(a.k.a. Shannon-Hartley Theorem)

Channel Capacity(a.k.a. Shannon-Hartley Theorem)

Claude Shannon Ralph Hartley

Power Line CommunicationsPower Line Communications

Image SourceWikipedia

Transformers don't pass high frequency signals.

Power Lines act as AntennasPower Lines act as Antennas

Source: http://www.doobybrain.com/2008/02/03/electromagnetic-fields-cause-fluorescent-bulbs-to-glow/

Home Power Line NetworksHome Power Line Networks Possible using home wiringPossible using home wiring

Outside Step Down Transformer blocks further wired transmissionOutside Step Down Transformer blocks further wired transmission Signal radiates off internal house wiringSignal radiates off internal house wiring

Netgear claims 500 MbpsNetgear claims 500 Mbps

Normalized Propagation DelayNormalized Propagation Delay NPD = NPD = End-to-End Propagation Delay End-to-End Propagation Delay

Average time to inject a Packet Average time to inject a Packet NPD > 1 NPD > 1

1 or more packets can simultaneously be in transit1 or more packets can simultaneously be in transit If NPD = 5, 5 average sized packets can be physically on the lineIf NPD = 5, 5 average sized packets can be physically on the line

NPD < 1 NPD < 1 Packet front end hits far side before back end transmittedPacket front end hits far side before back end transmitted

Transmitter ReceiverHigh SpeedLow Speed

Types of Traffic...Types of Traffic... Computer DataComputer Data

Bursty Bursty Highly sensitive to errors Highly sensitive to errors Not as time sensitive as voice or video Not as time sensitive as voice or video

Interactive Voice/VideoInteractive Voice/Video Fixed Rate (if not compressed) Fixed Rate (if not compressed)

*Not very sensitive to errors*Not very sensitive to errors Fixed or Variable Rate (if compressed) Fixed or Variable Rate (if compressed)

*Sensitive to errors*Sensitive to errors Time Sensitive Time Sensitive

IEEEIEEE Institute for Electrical & Electronics Institute for Electrical & Electronics

EngineersEngineers Largest Technical Organization in the WorldLargest Technical Organization in the World Promotes betterment of Electrical Promotes betterment of Electrical

EngineeringEngineering Journals & MagazinesJournals & Magazines ConferencesConferences StandardsStandards

IEEE 802.3 Ethernet IEEE 802.3 Ethernet Based on late 1970’s technologyBased on late 1970’s technology Covers OSI Layers 1 & 2Covers OSI Layers 1 & 2 10 Mbps Line Speed10 Mbps Line Speed Logical BusLogical Bus Designed to move Computer DataDesigned to move Computer Data The various 802.3 flavors dominate the The various 802.3 flavors dominate the wiredwired LAN LAN

Serial Bit Stream: NRZ CodingSerial Bit Stream: NRZ Coding

time

+1

volts

0

-1

T

0 0

LogicOne

LogicZero

Called ‘Non Return to Zero’because voltage never dwellson zero volts.

T

Ethernet Uses Manchester CodingEthernet Uses Manchester Coding

time

+1

volts

0

-1

T

0 0

LogicOne

LogicZero

All symbolshave a transitionin the middle.

Ethernet Uses Manchester CodingEthernet Uses Manchester Coding

time

+1

volts

0

-1

T

High Pass Filters Emphasize Change

High Pass Filter OutputHigh Pass Filter Output

time

+1

0

-1

Rectify (Absolute Value)Rectify (Absolute Value)

time

+1

0

-1T

Result always has pulses T seconds apart.Useful for receiver synchronization.

What is CSMA/CD?What is CSMA/CD? Polite ConversationPolite Conversation

One node active at a timeOne node active at a time No deliberate interruptionsNo deliberate interruptions Collisions sometimes occur after a pauseCollisions sometimes occur after a pause

802.3 Back-Off Algorithm802.3 Back-Off Algorithm choose random numberchoose random number

1st Collision1st Collision 0, 10, 12nd Collision2nd Collision 0, 1, 2, 30, 1, 2, 33rd Collision3rd Collision 0, 1, ..., 6, 70, 1, ..., 6, 74th Collision4th Collision 0, 1, ..., 14, 150, 1, ..., 14, 15

10th Collision10th Collision 0, 1, ..., 1022, 10230, 1, ..., 1022, 1023

15th Collision15th Collision 0, 1, ..., 1022, 10230, 1, ..., 1022, 102316th Collision16th Collision PuntPunt

Wait (Random Number*.0000512) secondsWait (Random Number*.0000512) seconds