ES 442 Lecture 1 1

EE442 Introduction An overview of modern communications

EE 442 Analog & Digital Communication Systems

Lecture 1

EE 442 Lecture 1 2

The Telegraph Revolution

Near instantaneous communication Adopted worldwide Became the Victorian Internet Used by railroads, newspapers, financial organizations, businesses of all kinds, Used in the Civil War by both North and South

EE 442 Lecture 1 3

Class Question: Name some modern communication systems that are in wide use today?

What interests you most in communications systems?

http://peryphon-dev.com/ta-3012-special-forces-full-duplex-wired-communication-system/

EE 442 Lecture 1 4

Public Switched Telephone Network (PSTN) – voice, fax, modem

Radio and TV broadcasting

Citizens’ band radio; ham short-wave radio; radio control; etc.

Computer networks (LANs, MANs, WANs, and the Internet)

Aviation communication bands; Emergency bands; etc.

Satellite systems (Military communications)

Cable television (originally CATV) for video and data

Cellular networks (4 generations – Most recent is LTE or 4G)

Wi-Fi LANs

Bluetooth

GPS

Selected Communication Systems In Operation Today

And of course many, many more . . . .

Signals Carry Content in Communication Systems

5 EE 442 Lecture 1

Data, messages, and information (i.e., useful content) sent from transmitter to receiver over a channel using electrical signals.

A SIGNAL is a sequence of symbols encoding the transmitted message.

Today’s communication systems mostly use electrical signals that are time-varying, electrical quantities (e.g., voltages, currents, and electro-magnetic field quantities in wireless) where the time variations encodes (i.e., represents) the data, message or information.

Important non-electrical signals include acoustic (voice and music).

A well-defined language or code is required between sender and receiver for communication. For digital signals we use various digital codes (e.g., binary).

For a signal to be considered as information we require:

(1) Accurate and timely, (2) Have a specific and organized purpose or focus, and (3) Results in increased understanding or decrease in uncertainty.

EE 442 Lecture 1 6

Advantages of Digital Over Analog

Reading: Lathi & Ding; Section 6.2.1 on pages 321 and 322.

1. Digital is more robust than analog to noise and interference†

2. Digital is more viable when using regenerative repeaters

3. Digital hardware is more flexible by using microprocessors and VLSI

4. Can be coded to yield extremely low error rates with error correction

5. Easier to multiplex several digital signals than analog signals

6. Digital is more efficient in trading off SNR for bandwidth

7. Digital signals are easily encrypted for security purposes

8. Digital signal storage is easier, cheaper and more efficient

9. Reproduction of digital data is more reliable without deterioration

10. Cost is coming down in digital systems faster than in analog systems and DSP algorithms are growing in power and flexibility

† Analog signals vary continuously and their value is affected by all levels of noise.

SNR = signal-to-noise ratio

DSP = digital signal processing

VLSI = very large-scale integration

EE 442 Lecture 1 7

Electrical Signals

found in Communication

Systems

Electrical & Optical Signals Dominate Communication

ES 442 Lecture 1 8 http://en.wikipedia.org/wiki/Carbon_microphone

Vo

ltag

e (V

)

Front contact

Button

Back contact

Diaphragm

V

Sound

waves

Resistive carbon layer

+

─ Bat

tery

Word: “erase”

Expanded view of voltage waveform

A microphone is a “transducer”

Carbon-Granular Microphone Inventor: Thomas Edison 1877

voltage waveform

Example: Human Speech is Analog Signal

ES 442 Lecture 1 9

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/ps8537/prod_white_paper0900aecd806fa57a.html

0 Hz 300 Hz 3,400 Hz 4,000 Hz 7,000 Hz

Voice energy

Telephone Band Filter Shape

Voice Bandwidth 300 Hz to 3,400 Hz

Voice Channel 0 Hz to 4,000 Hz

Frequency f (Hz)

Ene

rgy

Voice Bandwidth (Bell Determined 3400 Hz Was Adequate

ES 442 Lecture 1 10

FREQUENCY in Hertz (Hz)

20 50 100 200 500 1K 2K 5K 10K 20K

120

100

80

60

40

20

0

SO

UN

D IN

TEN

SITY

LEV

EL in

de

cib

els

(d

B)

Human Hearing Chart

Discomfort Threshold

Speech

Hearing Threshold

Music

aging

Presbycusis is loss of hearing with age.

Acoustic signals

Human Speech Intensity and Frequency Boundaries

ES 442 Lecture 1 11

Discussion: Electrical-Based Communication Systems

Why do electrical systems dominate modern communication systems?

Electrical variables = Voltage, current, electric-field & magnetic field.

This is not electrical communication.

ES 442 Lecture 1 12

Communication Systems

EE 442 Lecture 1 13

Electromagnetic Spectrum (There is only one in the universe)

http://www.mondialbioregulator.co.uk/electromagnetic-spectrum-mondial-bioregulator.asp

The gateway to WIRELESS.

ES 442 Lecture 1 14 National Telecommunications & Information Administration (NTIA) is an agency of the United States Department of Commerce http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf

AM radio

FM radio

3 kHz

300 GHz 30 GHz

3 GHz

300 MHz

30 MHz

3 MHz

300 kHz

30 kHz

Frequency Allocation by FCC

EE 442 Lecture 1 15

Radio and Optical Windows in Atmosphere

http://www.spaceacademy.net.au/spacelink/radiospace.htm

Just as sight depends upon the “Visible Window,” wireless communication depends upon the existence of the “Radio Window” in the EM spectrum.

Ozone & Molecular

Oxygen

Water & Carbon Dioxide

Charged Particles

Radio

Window

Frequency

Op

acit

y

Partial IR Windows

Visible Window

Microwave Windows

Increasing frequency

0 %

MHz PHz GHz THz

100 %

30 300 3 30 300 3 30 300 3 30 3

EE 442 Lecture 1 16

Total, Dry Air and Water-vapor Zenith Attenuation from Sea Level

V-band is 50 to 75 GHz W-band is 75 to 100 GHz

W-band & V-band used in satellite communications

Why W/V band for satellite communications?

W & V bands have no crowding in frequency, hence, this provides reduced interference, large bandwidth availability, reduced antenna and electronic components size, and more security in point-to-point links due to smaller beamwidths.

Dry air

Water vapor

Total

Frequency (Hz)

1

0.1

0.01

10

100

1 10 100 350 0.001

Zen

ith

Att

en

uat

ion

(dB

) 1000

Radio Window

EE 442 Lecture 1 17

Example: Unlicensed Spectrum – ISM and & UHII RF Bands

Band

ISM I

ISM II

ISM III

Frequency Range

902 – 928 MHz

2.4 – 2.4835 GHz

5.725 – 5.85 GHz

UNII I

UNII II

UNII III

5.15 – 5.25 GHz

5.25 – 5.35 GHz

5.725 – 5.875 GHz

Applications

Cordless phones; 1G Wireless Cellular

Wi-Fi; Bluetooth; ZigBee; Microwave ovens

Cordless phones; Wireless PBX

Wi-Fi 802.11a/n

Short-range indoor; Campus applications

Long-range outdoor; Point-to-Point links

ISM: Industrial, Scientific & Medical & UNII: Unlicensed National Information Infrastructure

Frequency (GHz) 1

UNI I ISM II

2 4 3 6 5

ISM I UNI II ISM III UNI III

EE 442 Lecture 1 18

Wireless Communication: Radiation from Dipole Antenna

Single Direction Shown Here

http://askthephysicist.com/ask_phys_q&a_old5.html

antenna

dipole

Electric & Magnetic Fields

EE 442 Lecture 1 19

Channel Limitations and Challenges

Propagation loss – The greater the distance, the greater the loss (All channels are lossy unless they have gain built into them) Frequency selectivity – Most media are transmitted over selective frequency bands (FCC assigns these bands) Time variation – Many channels have natural varying conditions which change transmission properties (e.g., temperature changes and moisture content) Nonlinearity – Ideally a channel is linear; however, exceptions exist such as satellite communication through the ionosphere Shared usage – Most channels are not dedicated to a single user so they must contend with multiple users Noise – All channels contribute noise to the signal as it travels through the medium Interference – Channels can pick up adjacent communication signals and noise which interfere with the intended signals

All of these influence and/or limit the choice of modulation schemes & transmitter/receiver (transceiver) design.

EE 442 Lecture 1 20

Radio Waves

Mobile Station: MS

Also, Moisture in atmosphere causes variations in radio signal strength.

Multipath Reception

Base Transceiver

Station

Challenges in Wireless: Fading in Cellular Telephony

Transmitter will . . . Encode message data Add a carrier signal (modulation) Set signal parameters for channel transmission and transmit

Receiver will . . . Receive signal Remove the carrier signal (demodulation) Decode the data to put it into format for destination

Information Source

Transmitter

Information Destination

Receiver

Message being sent

Message received

Signal Transmitted

Signal Received

Noise Message put into a format

appropriate for transmitting over channel

Signal retrieved from channel

and converted into a format

appropriate for the destination

Wireline, EM waves

or Fiber

Noise distorts

signal with random

additions

Channel

Shannon-Weaver Model for Communication

21 EE 442 Lecture 1

From ES 101A

EE 442 Lecture 1 22

Radio Superheterodyne Receiver

Mixer RF

Amplifier & Tuner

IF Amplifier

AF Amplifier

Demod-ulator

Filter

Local Oscillator

Audio Speaker

Antenna

frequency f

Am

plit

ud

e IF

RF

LO

Receiver

EE 442 Lecture 1 23

Why do we cover Analog if Digital is so dominant?

1. The world is fundamentally an analog world (People respond

primarily to analog symbols, images & sounds)

2. Digital signals are actually “analog signals” just encoding “digital data”

(bits still must be converted to physical waveforms)

3. Digital communication systems make use of components leveraged

from analog communication systems (e.g., ADC & DAC converters,

mixers, amplifiers and antennas)

4. Analog communication systems illustrate high-level issues and principles

(especially true as we push data rate limits)

5. Analog communication systems are still in use (e.g., AM and FM radio)

IMPACT: We must convert analog data to digital data and vice versa.

ES 442 Lecture 1 24

time time

amp

litu

de

amp

litu

de

0 1 0 1 . . . 1 1 0 1

All signal waveforms are analog – the difference is what they represent!

Analog Signals versus Digital Signals

• Analog Signals represent the values of physical parameters which vary in time.

Amplitude can be any value within a range of values, and

Amplitude is time-varying

• Digital Signals represent a sequence of numbers.

The values restricted to a set of discrete values

Example: Binary signal with only two values (1 and 0).

Amplitude is time-varying but

magnitude is not important

EE 442 Lecture 1 25

ADC Process: Sampling, Quantizing & Encoding

Analog to Digital Data Conversion (ADC) Process

Note: “Discrete time” corresponds to the timing of the sampling.

Sample Quantize Encode Analog Signal Captured

Sampled Data Values

Quantized Sampled

Data

Digital Signal

Analog signal is continuous

in time & amplitude

Discrete time values:

few amplitudes from analog

signal

Now have discrete Values in

both time & amplitude

Now have the digital

data which is the final

result

Sampling selects the data points we use to create the

digital data

Quantizing chooses the amplitude

values used to encode

Encoding assigns binary

numbers to those

amplitude values

time

am

plit

ud

e

0100101101011001 1110101010101000 0100011000100011 0101001111010101 1110110111010001

time

amp

litu

de

time amp

litu

de

EE 442 Lecture 1 26

To communicate sampled values, we send a sequence of bits that represents the quantized value.

For 16 quantization levels, 4 bits are required.

PCM can use a binary representation of value.

The PSTN (1976) uses PCM

Figure 1.5 on page 8 of Lathi & Ding

Pulse Code Modulation

EE 442 Lecture 1 27

Examples of Digital Encoding

Format Symbols per Bit

Self-clocking?

Duty Factor (%)

NRZ

RZ

NRZI

Manchester (Biphase L)

Miller

Biphase M (Bifrequency)

1

2

1

2

1

2

No

No

No

Yes

Yes

Yes

0-100 %

0-50 %

0-100 %

50 %

33-67 %

50 %

And many, many more are possible . . . .

EE 442 Lecture 1 28

Data Rate Limits (Shannon Capacity) – Noise Dependent Data rate R is limited by channel bandwidth, signal power, noise

power and distortion

Without distortion or noise, we could transmit without limit in the

data rate. However, this is never reality.

The Shannon capacity C is the maximum possible data rate for a

system with noise and distortion

Maximum rate approached with bit error probability close to 0. For

additive white Gaussian noise (AWGN) channels,

Shannon obtained C = 32 kbps for telephone channels

Nowhere near capacity in wireless systems

2C log 1 in bits per secondsignal power

Bnoise power

READ: Lathi & Ding, section 1.3.2 on pages 10-11.

EE 442 Lecture 1 29

Additive White Gaussian noise Corrupts Signals

“White” means noise power is uniform over all frequencies

Digital signal corrupted by White Gaussian noise

EE 442 Lecture 1 30

Digital Signal Errors From Noise and Interference

EE 442 Lecture 1 31

Analog Signal Corrupted by Noise

Question: Is it possible to recover the analog signal from noise after it has been corrupted (i.e., signal + noise waveform is shown below)?

Signal + Noise

EE 442 Lecture 1 32

The Four Primary Enablers of the Communication Age (from ES 101A “Communications in the Information Age”)

Electric Power Generation (1880s)

Alessandra

Volta – Battery (1800)

1. Harnessing of Electricity

Guglielmo Marconi Radio Waves

( began in 1896 with wireless telegraphy )

2. Radio Waves

3. Digitization 4. Transistors & Integrated Circuits

Telegraph & Telephone 1844 1876

Started in 1940s (but accelerated

in the 1970s) Moore’s Law

Transistor 1948 IC invented 1958

(Jack Kilby & Robert Noyce)

EE 442 Lecture 1 33

Selective History of Communication Technologies

1794 – Claude Chappe develops an armature signal telegraph 1837 – First commercial electrical telegraph was Cooke-Wheatstone telegraph 1837 – Samuel Morse independently develops and patents an electrical telegraph (leads to Morse Code) 1876 – Alexander Graham Bell demonstrates voice-based telephone 1896 – Wireless telegraphy (radio telegraphy) by Guglielmo Marconi 1901 – First transatlantic radio telegraph transmission (Marconi) 1906 – First AM radio broadcast by Reginald Fessenden 1920 – First commercial radio stations 1921 – First mobile radio service (Detroit Police Department) 1928 – First television station in United States (W3XK) 1935 – Edwin Armstrong demonstrates FM radio 1947 – Bell Telephone laboratories proposed cellular concept 1947 – BTL invents and demonstrates solid-state transistor 1958 – Integrated circuit is invented (Jack Kilby at Texas Instruments) 1984 – AMPS cellular mobile service by Motorola 1991 – GSM cellular service (digital) service begins 1997 – IEEE 802.11(b) wireless LAN standard