LEC 4

Question 1

Represent digital data using digital signals

Answer 1

digital-to-digital conversion

Question 2

3 techniques in conversion:

Answer 2

– Line Coding
– Block Coding
– Scrambling

Question 3

number of data elements sent in 1 second

unit : bits per second

Answer 3

data rate

Question 4

number of signal elements sent in 1 second

unit : baud

Answer 4

signal rate

Question 5

T/F

Although the actual bandwidth of a digital signal is infinite, the effective bandwidth is finite.

Answer 5

true

Question 6

For the correct interpretation of the signals

received from the sender, bit intervals of the receiver must match the sender’s bit intervals

Answer 6

Self-synchronization

Question 7

0s and 1s are significant conditions; no other neutral or rest condition,

e.g. no middle signal state
other than 0s and 1s

Answer 7

NRZ (non-return-to-zero)

Question 8

In ____ the level of the voltage determines the value of the bit.

Answer 8

NRZ-L

Question 9

In ____ the inversion or the lack of inversion determines the value of the bit.

Answer 9

NRZ-I

Question 10

T/F

NRZ-L and NRZ-I both have an average signal rate of N/2 Bd.

Answer 10

tRUE

Question 11

T/F

There are DC components that carry a high level of energy

Answer 11

TRUE

Question 12

T/F

Power density is very high around frequencies close to 0.

Answer 12

TRUE

Question 13

In Manchester and differential Manchester encoding, the transition at
the middle of the bit is used for ____

Answer 13

synchronization

Question 14

T/F
The minimum bandwidth of Manchester and differential Manchester is 2 times
that of NRZ

Answer 14

TRUE

Question 15

T/F

In bipolar encoding, we use three levels: positive, zero, and negative.

Answer 15

TRUE

Question 16

Neutral voltage represents 0 while positive and negative voltages represent 1

Answer 16

AMI (Alternate Mark Inversion)

Question 17

Neutral voltage represents 1 while positive and

negative voltages represent 0

Answer 17

Pseudoternary

Question 18

• Developed as an alternative to NRZ
  – Same signal rate as NRZ but there’s no DC
  component

Answer 18

Bipolar schemes

Question 19

In ____, a pattern of m data elements is encoded as a pattern of n signal elements in which 2m ≤ Ln.

Answer 19

mBnL schemes

Question 20

Used in Digital Subscriber Line (DSL) technology

Answer 20

2B1Q

Question 21

Used in 100BASE-4T or 100BASE-T4 cable (early

implementation of Fast Ethernet)

Answer 21

8B6T

Question 22

four-dimensional five-level pulse amplitude

modulation

Answer 22

4D-PAM5 scheme

Question 23

MLT-3

Answer 23

Used in 100BASE-TX, predominant form of

Fast Ethernet

Question 24

______is normally referred to as mB/nB coding; it replaces each m-bit group with an
n-bit group.

Answer 24

Block coding

Question 25

___is part of a family of errorcorrecting codes in data transmission

Answer 25

blcok coding

Question 26

- reduce synchronization problems | – inherent error detecting

Answer 26

purpose of block coding

Question 27

T/F | NRZ-I has good signal rate, but it has a synchronization problem

Answer 27

true

Question 28

t/f | Long sequence of repeating bits may lead to loss of synchronization on the receiver side

Answer 28

true sol'n: Solution : change the bit stream prior to NRZ-I encoding

Question 29

T/F | 4B/5B encoding in combination with NRZ-I solves the problem of synchronization

Answer 29

true However: – Increases the signal rate of NRZ-I – Does not solve the DC component problem of NRZ-I

Question 30

where most significant five bits are fed

Answer 30

5B/6B encoder

Question 31

where the least significant 3 bits are fed

Answer 31

3B/4B encoder

Question 32

prevents a long sequence of 1s or 0s in the combined block

Answer 32

disparity controller

Question 33

wide bandwidth requirement (not suitable for long-distance communication)

Answer 33

biphase schemes

Question 34

DC component problem (not | suitable for long-distance communication)

Answer 34

Block coding and NRZ line coding

Question 35

narrow bandwidth and no DC component problem

Answer 35

Bipolar AMI encoding

Question 36

TO DO : avoid long sequence of repeating 0s solution: _____

Answer 36

scrambling

Question 37

T/F | Digital Signal is superior to an Analog Signal

Answer 37

TRUE 2 techniques: pulse code modulation delta modulation

Question 38

continuous-time to discrete-time signal

Answer 38

sampling

Question 39

The amplitude of a series of signal pulses is used to encode message information

Answer 39

PAM SIGNAL

Question 40

amplitude is restricted to a prescribed set of values

Answer 40

Quantized signal

Question 41

3 Different Sampling Methods | for PCM

Answer 41

IDEAL NATURAL FLAT-TOP

Question 42

pulses from the analog signal are sampled

Answer 42

ideal

Question 43

sequence of samples retains the shape of the analog signal

Answer 43

natural

Question 44

the top of the samples have constant amplitude

Answer 44

flat-top

Question 45

T/F According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal.

Answer 45

TRUE

Question 46

T/F

Answer 46

● PCM finds the value of the signal amplitude for each sample. ● DM finds the change from the previous sample.

Question 47

_____ we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte.

Answer 47

asynchronous transmission

Question 48

___we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits

Answer 48

synchronous transmission

Question 49

Isochronous transmission guarantees that the | data arrive at a fixed rate.

Answer 49

ISOCHRONOUS