Professor Tarek SaadawiRm 529X7263

Office Hours: Thursday 12 – 1:30Also random in Tuesday

Local and Metroplitan Area Networks(I-7000)

Input Transmitter channelOutputDevice

Receiverx(t) r(t) ~I(t)I(t)

Code [ A 1 0 0 0 0 0 1 ]EncodeModulation, amplification, Fitering Fig 1 Basic Model For a Communication System

I (t) = Analog

Digital

X (t) = Analog

Digital

Introduction to Digital/Data Communications Systems

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Figure 2.6 Problems caused by Clock Drift

Receiver withSlow Clock

x x x x

x x x x x xReceiver withFast Clock

Transmitted’signal

Transmitter’Clock

0 0 1 0

0 0 01 1

0 01

Time

ASYNCHRONOUS SYNCHRONOUS 20 mA current loop BISYNC

EIA RS 232C HDLCSerial EIA RS-422, 423, 499 ISDN LAP-d

EIA RS 485 IEEE 802 standards _

Parallel IEEE STD 488 – 1978 MicroprocessorInterfaces

_

Figure 2.9 Typical data transfer interfaces

Encoder Decoder

Bit stream to betransmitted b(t)

transmitted signal d(t)

transmission link

Modulator Demodulator

Bit stream to betransmitted b(t)

transmitted signal a(t)

transmission link

Figure 2.11 bits are modulated into analog signaling

b(t)

b(t)

Figure 2.10 bits are encoded digital signaling

Bit stream to be transmitted

1 0 0 1 1 0 1

+v

-v

-v

+v

0

0

-v

RZ

NRZ

NRZ1

Manchester

Leads to out of

synch, DC voltage,

Differential encoding;

comparing the polarity of

adjacent bits, more reliable

to detect a transition than

to compare a threshold

Self-clocking, 2 symbols per

bit (baud), 10 Mbps means 20

MBauds, η=50%

•

•

•DifferentialManchester

Alternating MarkInversion

Duo binary

Figure 2.12

3-levels, binary

zero is zero

voltage, binary 1

alternates

“1” = previous “1” if even

zeros, otherwise the complement

Reasons for line coding: Freq spectrum; freq spectrum, synchronization, better performance under noisy environment

Bit stream to be transmitted

1 0 0 1 1 0 1

0 1 0 0 1 0 1 0

X

(a) ASK

A1 cos(wt + θ ) b(t) = 1A2 cos(wt + θ ) b(t) = 0

•

N

b(t)

A cos (2πf t +θ )

(b) FSK

(c) PSK

A cos (2πf1 t +θ )b(t)A cos (2πf2 t +θ )b(t)

A cos (2πf1 t +θ )b(t)A cos (2πf2 t +1800 ) b(t) = 0

frequency f1

frequency f2

1800 phaseshift

1800 phaseshift

X

N

b(t)multiplication

x(t)

Carrier

Q – PSK b(t)A cos (wt + 0 ) 0 0A cos (wt + 90 ) 0 1A cos (wt + 180 ) 1 1A cos (wt + 2π ) 1 0

M-ary – PSK

Figure 2.14 Digital Signal Modulation Techniques

Mary PSK:

x(t) = A con ( 2πft + { 2πf2 / M } ) , k = 0,1,…….., M.

M = 2 PSKM = 4 QPSK

Anolog

Digital

Anolog

ASK, PSK, FSK, MSK(Moderns)

AM, FM, PM Modulator(transmitter) Anolog

Digital

PCM, Delta Modulator

RZ, NRZ, NRZ1codec, Digital transmitter

Type of signal transmittedInformation

to be transmitted

Figure 2.16 Example of Information Signaling format and the devices used.

+ A B C+G3 = 1

G2 = 1G1 = 0G0 = 1Input

(10011)

Shift Register G(X) = X3 + X2 + 1 XOR r = 3 0 0 0 0 1 1 1 0 1 1 1 0

Shift RegisterContent

Step Input A B C 0 0 0 0 0 1 1 1 0 0 2 1 1 1 0 3 0 0 1 1 4 0 1 0 0 5 1 1 1 0 6 0 0 1 1 7 0 1 0 0 8 0 0 1 0