professor tarek saadawi rm 529 x7263 office hours: thursday 12 – 1:30 also random in tuesday local...
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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