ECE 4710: Lecture #1 1 Communication Systems Designed to transmit information between two points Electrical systems do this via electrical signals

ECE 4710: Lecture #1 1

Communication Systems

Designed to transmit information between two points Electrical systems do this via electrical signals

Time-varying voltage (or current) in electrical circuit» “Wired” communication

Time-varying EM wave propagating through air/space» “Wireless” communication

Transmission of information implies that message is not known ahead of time random Randomness (entropy) is proportional to information

content


Communication Systems

Design and selection of information bearing waveforms is critical to successful communication

Waveform design/selection depends on: Signal Bandwidth (Bs)

Information Data Rate (Rd)

Transmission Center Frequency (fc)

Signal Power/Energy (Ps)

Resistance to Noise/Interference (N) Complexity/Cost to Design Tx/Rx Circuits


Communication History

Year Event Inventor/Comment

1837 Telegraph Samuel Morse

1864 EM Theory James Maxell

1876 Telephone A.G. Bell

1901 Radio Transmission G. Marconi

1921 Mobile Radio

1928 Television P.T. Farnsworth

1933 Frequency Modulation (FM) E.H. Armstrong

1945 First Computer Univ. of Penn.

1948 Information Theory Claude Shannon

1948 Transistor Shockley et al.

1950 Error Coding Hamming


Communication History

Year Event Inventor/Comment

1958 Integrated Circuit Jack Kilby (TI)

1965 Satellite Communications

1971 Microprocessor Intel

1972 Cellular Radio Concept Motorola/Bell Labs

1981 Personal Computer IBM

1983 1st Generation (1G) Cellular Analog AMPS

1989 GPS Satellites U.S. Military

1991 2G Digital Cellular GSM in Europe

1995 WWW and Internet

1998 2G CDMA Cellular Qualcomm/Sprint PCS

2003 3G Cellular Standards Whole World


Analog vs. Digital

Information Source Analog: continuous range of states

» Microphone: output voltage signal with continuous range of amplitudes (infinite number of voltages)

Digital: finite set of possible states» Computer Keyboard: finite set of characters

Waveform = signal voltage vs. time Analog continuous amplitude Digital discrete set of amplitudes


Typically uses BOTH analog AND digital waveforms Analog: carrier waveform (sinusoid) for transmission Digital: discrete values for amplitude, frequency, or phase

used to represent information bits Binary Digital Waveform

2 states for each digital symbol, e.g. 0, 1

M-ary Digital Waveform M-states for each symbol

# Bits/Symbol = log 2 (M)

Digital Communication System

0 1 0 1 0 1 0 1

00 01 00 10 00 11 00 01

M = 4 states 2 bits/symbol


Deterministic vs. Random

Waveform Classification Deterministic: waveform modeled or represented completely as a

function of time, e.g. s (t) = A cos (t + ) Random/Stochastic: cannot be completely specified as a function of

time

Recall that randomness = information Waveforms must be random to carry significant information

Source/Information Waveform: each symbol can be deterministic but information stream is random

Noise is also a random signal Probability/Statistics must be used to analyze

performance of any communication system


Digital communication systems have MANY advantages over analog systems including: Data encryption for security/privacy Combine multiple information types (voice, video, data) on

a single transmission channel Resistant to noise, fading, and interference

» Small error probability even with large interference Error detection and correction using digital codes Implementation using all digital circuits

Digital Communication System


Basic Communication System

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Information Source

BasebandSignal

Processing

Modulation & CarrierCircuits

TransmissionChannel

Demodulation & CarrierCircuits

BasebandSignal

Processing

Information Sink

Noisen (t)

m (t) s (t) r (t) m (t)

Transmitter (Tx) Receiver (Rx)

Goal: Design system to transmit information, m(t), with as little deterioration as possible within design constraints of signal power, signal bandwidth, and system cost


System Components

Baseband signals signal centered at f = 0 m(t) : input information signal (voice, data, video, etc.) m(t) : received information signal distorted/corrupted by

noise, interference, non-linearities, etc.

Baseband Signal Processing Encoding of information “Source coding” Filtering to minimize signal bandwidth Error coding to protect information “Channel Coding”

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System Components

Tx Carrier Circuit Converts processed baseband signal into frequency band

that is appropriate for transmission through channel Tx output s(t) is called a “bandpass” signal

» Carrier frequency, fc, is center frequency of bandpass signal

m(t) s(t) conversion or mapping is called “modulation” Channel : Two major categories

Wire coaxial, twisted pair, & fiber optic cables Wireless mobile radio (cellular, 3G, 4G, etc.), terrestrial radio/TV

broadcasts, satellite radio/TV broadcasts, WiFi, bluetooth, etc. Introduces significant attenuation, noise, and possibly distortion and

other impairments (e.g. interference)


System Components

Channel Impairments Attenuation, multipath echoes, fading, noise, interference,

etc. Channel characteristics can be fairly stable (wired) or

change rapidly as function of time (mobile radio)» Time-varying channel is difficult to model

Noise» Man-made: computers, motors, car ignition, other users

(cellular phone)» Natural: thermal “background” noise, lightening, etc.


System Components Receiver Carrier Circuit (Rx)

Takes corrupted signal from channel, amplifies, filters, etc. and then converts down to baseband signal demodulation (mod/dem = modem)

Rx Baseband Signal Processing Cleans up distorted baseband signal and delivers estimate of

the source information signal m(t) Filtering, bit detection, error detection/correction

Performance measures Analog output signal-to-noise (S/N) ratio Digital probability of bit error or “Bit Error Rate (BER)”

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Documents

ECE 4710: Lecture #1 1 Communication Systems Designed to transmit information between two points Electrical systems do this via electrical signals