Professor Tarek Saadawi Rm 529 X7263 Office Hours: Thursday 12 – 1:30 Also random in Tuesday Local and Metroplitan Area Networks (I-7000)

Input Transmitterchannel Output Device Receiver x(t) r(t) ~I(t)I(t) Code [ A ] Encode Modulation, amplification, Fitering Fig 1 Basic Model For a Communication System I (t) = Analog Digital X (t) = Analog Digital Introduction to Digital/Data Communications Systems

Figure 2.6 Problems caused by Clock Drift Receiver with Slow Clock xxxx xxxxxx Receiver with Fast Clock Transmitted’ signal Transmitter’ Clock Time

ASYNCHRONOUS SYNCHRONOUS 20 mA current loopBISYNC EIA RS 232CHDLC Serial EIA RS-422, 423, 499 ISDN LAP-d EIA RS 485IEEE 802 standards _ Parallel IEEE STD 488 – 1978Microprocessor Interfaces _ Figure 2.9 Typical data transfer interfaces

EncoderDecoder Bit stream to be transmitted b(t) transmitted signal d(t) transmission link ModulatorDemodulator Bit stream to be transmitted b(t) transmitted signal a(t) transmission link Figure 2.11 bits are modulated into analog signaling b(t) Figure 2.10 bits are encoded digital signaling

Bit stream to be transmitted 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%

Differential Manchester Alternating Mark Inversion Duo binary Figure 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

X (a) ASK A 1 cos(wt + θ ) b(t) = 1 A 2 cos(wt + θ ) b(t) = 0 N b(t) A cos (2πf t +θ ) (b) FSK (c) PSK A cos (2πf 1 t +θ )b(t) A cos (2πf 2 t +θ )b(t) A cos (2πf 1 t +θ )b(t) A cos (2πf 2 t ) b(t) = 0 frequency f 1 frequency f phase shift phase shift

X N b(t) multiplication x(t) Carrier Q – PSK b(t) A cos (wt + 0 ) 0 0 A cos (wt + 90 ) 0 1 A cos (wt ) 1 1 A 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 PSK M = 4 QPSK Anolog Digital Anolog ASK, PSK, FSK, MSK (Moderns) AM, FM, PM Modulator (transmitter) Anolog Digital PCM, Delta Modulator RZ, NRZ, NRZ1 codec, Digital transmitter Type of signal transmitted Information to be transmitted Figure 2.16 Example of Information Signaling format and the devices used.

+ ABC + G 3 = 1 G 2 = 1 G 1 = 0G 0 = 1 Input (10011) Shift Register G(X) = X 3 + X XOR r = Shift Register Content Step Input A B C